For quite a lot of Black Sabbath songs, Tony Iommi tunes each string down by 3 frets to get 'C# tuning'. This is one of those songs.

Low C# : F# : B : E : G# : C#

The good news is that the song is actually not too hard to learn. The 3 main riffs are quite easy and definitely good practice for aspiring rock guitarists. If you don't want to downtune - just practice in standard tuning. It will still sound good (just higher). The more important thing is to get those fingers trained. So let's break the song into it's few riffs:

Riff 1 - This is the main riff of the song. It's surprisingly simple too. However, you will need to take it slowly at first until your fingers get the hang of it. Then work on building speed last (as usual).

Riff 2a - This always follows Riff 1 and is also very straightforward. It's just 2 downstrokes on the open F# string, followed by 3 bends. This is the easiest riff in the whole song. Tony Iommi recorded 2 guitars to play this riff - if you listen carefully to the middle bend, you can hear a second guitar plays a slightly different bend....

Riff 2b - This is what Tony Iommi plays with his second guitar during the recording. It's exactly the same as the previous riff, except the middle bend is different (which we show this time round). So, the only real difference between these two riffs is that 1 note. Play whichever variation you prefer the sound of. Also, add some vibrato just after the bends to fatten the sound a little more.

Riff 3 - This is the chorus riff. Again, it's nothing too difficult as long as you take your time with it. When playing the ActionTab you should be able to see that the riff is basically the same fingerings shifted up and down the neck by 2 frets each time it repeats.

Solo - Another thing Tony Iommi likes to do is multiple guitar solos all at once. This is one of those songs where he does just that. So, rather than show each individual guitar part (which you'd be unlikely able to play anyway), we've condensed the various lead parts into a single solo.

Solo's aren't for everyone (especially beginners), so skip it unless you are ready and able. Just focus on getting the main rhythm guitar riffs right first - there's only 3 riffs for the whole song. Practice them and try out similar songs too. Use the Core Skills practice exercises. Only once your fingers are used to playing for a while should you worry about solo techniques. Always get good at rhythm guitar stuff (chords and riffs) before worrying about lead techniques!