This tutorial focuses on transcribing. For arranging, check Kabukibear's tutorial.
First thing is if you have headphones, definitely use them. It's just much clearer than speakers since the music is not traveling through the air.
Try to use an mp3 or some audio file. Most of the time mp3s are hard to find, but a lot of vgmusic is on youtube. Just put the url into this website http://www.mediaconverter.org/ and convert it into an mp3 to play on windows media player or something. This might seem like a minor point, but it is much easier to work with a song on wmp than youtube, becuase you can be more precise with the time scroller. Also you can slow down the song in wmp with ctr+shift+s and ctr+shift+n to go back to normal speed. This is useful for fast parts of a melody, but it also makes it harder to hear due to background noise. You should really only be using this for fast parts, not the whole song, especially if you are trying to figure out the rhythm.
Start out making tabs with just the melody. When I first started making tabs I think I might have let the song play one note, pause, figure out that note, write it down, and then do the same with each note. Do not do this. Before even beginning to make a tab, just listen to the song two or three times until you can memorize and play the melody in your head. Break it down into overlapping pieces, learn to play these pieces, then combine them together into larger pieces, and then into a whole. Once you can play the whole song, even if you can only play it really slowly, you'll know how the pieces fit together, and you'll (hopefully) have the most natural way of playing it. At this point, it should be committed to memory, so you can start writing it down.
You don't have to work that way, of course. If it's really complex, sometimes I have trouble fitting it all in my head without writing it down, and I break it down by sections instead, writing down each section as I go. You can break stuff down as much as you need to. Just make sure the sections ALWAYS overlap, because the hand movement between parts is just as important as the notes.
It might be a good idea to figure out what key you are in before trying to play the melody on guitar. Most of the notes should be non-accidental notes in that key. Remember that most melodies do not make big leaps between notes. From one note to the next might only be one, two, or three notes up the scale.
Pay attention to what direction the note is moving. Sometimes a tabber might figure out a melody one note at a time and put one note an octave too high or low. This is why you have to pay attention to the structure and movement of the melody (melodic contour). If one note plays and the following note sounds higher, then you obviously move up.
When transcribing for guitar, don't put all the notes on one string. A lot of people, when making their first tab, think it is easier to play a song with all the notes on the high e string. But that actually makes it more difficult, having to move up and down the neck. Try to minimize movement along the fretboard. You have six strings; use them!
A note on fast melodies: You should not be tackling a song with a very fast melody or even part of a melody is you are a beginner. But, one way to approach this might be to figure out the first note, then the last note of a certain phrase. Then count with you fingers while listening to the song how many notes play. From there, just fill in everything in between. With guitar songs such as a metal piece with shredding might sound difficult when listening, but often the guitarist is just playing a scale upwards or downwards very fast.
After you've written it down, listen to the whole thing, mentally reading along with it. This is the best way to make sure you didn't add any notes. Then play through the whole thing to check it. If you are making a tab with a program such as guitarpro,powertab, or tuxguitar, try playing the midi you made trough the program and the mp3 of the original song at the same time. Once you have the tempo and rhythm set, listen to make sure the notes match up.
Harmony and bass might be trickier to figure out, so stay away from those until you are able to transcribe melodies easily. After a while you should be able to pick apart the different instruments of a song.
One thing to note, especially when transcribing bass: you don't just identify notes by their fundamental frequencies (which you don't even always hear), but by their harmonics. Your ear is also better at recognizing non-bass frequencies, and even ignoring that, bass frequencies are less precise by nature (uncertainty principle).
If you're transcribing bass, you should make sure the tone is turned up on your instrument! Transcribing is not the time to try to make your instrument sound cool. You need to be able to hear your own notes accurately to tell if they're fitting the song you're playing along with.
For making an arrangement I generally just figure out the melody, the way described above, and then add bass or harmony from the source. And if the fingering doesn't work out you just have to make you own bass/harmonies that don't really sound like the original. Make sure you can easily reach both the melody and bass. If you have a tab program you can easily fool around with the frets, moving up or down to make easy fingerings.
Some additional stuff:
Obviously, make sure your instrument is in tune, intonated, not too loud, not too quiet, tone isn't rolled off.
If the song actually has a guitar in it, try to listen closely for hammer-ons, pull-offs,slides,bends,etc. Though these might be difficult to differentiate, so just try your best to match the song.
Consider learning music theory to understand chord structure. It's too complex for me to discuss here and I'm no expert on it.
The most common tab programs are guitarpro, powertab, and tuxguitar. If you want guitarpro (the only non-free one) then get version 5, not gp6. I prefer the way it exports text files.
And of course, getting good at transcribing takes practice and time. It only gets easier.