I want to help you out with this. As was mentioned earlier, this is a pretty simple song. It's a 12 bar blues in E minor with a distinctive riff. The 12-bar format is simple, but it takes a little bit of practice to internalize. This is truly the most important step in the process. Blues is all about the feel and movement of the blues change, and this step cannot be overlooked. There are many variations of the 12-bar form, but in this case it's your standard change. 4 bars Em, 2 bars Am, 2 bars Em, 1 bar Bm, 1 bar Am, 2 bars Em. That's the complete change. Each "bar" is one count of four. I would get comfortable strumming this pattern until you can move through it flawlessly, before placing the riff on top of it. You will not only accomplish learning this song, but one of the most common forms in music. You will likely use it for years to come. Once you can do this, now you should move on to the riff. I'll tab it out for you:

0-2------------0-------------0-2--------------- ----------0-2-----2--0------------------------- --------------------------3----------------------

The timing on this is key. I wish I could add it in for you, but it's a little hard to pull off in reddit's small reply box. Listen to the track, play this and feel it out. It'll come to you. Gary plays this riff over the Em chord in the change, then switches to strumming for the iv (Am) and v (Bm) chords. When moving to the Am chord, he uses both your traditional voicing and an Am7 voicing.

Gary's Am7 ----3 ----1 ----0 ----2 ----0 ----x

That just about does it. Basically, strum the change until you feel comfortable with it. Strum along to the track to get a feel for his time and rhythm. You will not be able to play this well unless you do. Do this ESPECIALLY if you want to sing the lyrics as well. Then, listen to the track and learn the riff using my tabs, tabs sourced from elsewhere, or your ear. Listen to how it falls in line with the time and changes, it'll come to you with practice. Let me know how this works out.