What specific materials do i need to soundproof my home recording studio?

It all depends on your budget and how elaborate you want to get. Professional studios spend a lot of money on soundproofing.

There are two purpoese of soundproofing 1) to inside sounds from getting outside the studio 2) to keep outside sounds from entering the studio. Most studios try to accomplish both, since drums and loud amps can disturb neighbors at the musicians most creative moments, and nobody wants the sounds of yelling neighbors, sirens, pounding on doors, megaphones from angry cops, etc. from getting into recordings.

Seriously... A couple of cost-effective methods would work. There is the "building within a building" which works well. Build an actual room inside your garage using sheetrock on both sides of the walls with insulation in the center. This is fairly effective most of the time. To ensure that sound doesn't make it through via "coupling," make 2x6 walls (using 2x6s at the ends) and stagger 2x4s with the studs in-between - using thicker insulation than as well. This method works wonders and is often used between apartments to block sounds.

Another way, is to double up on sheetrock, maybe putting some soft material in-between the layers.

Now the best (and most expensive) methods are using sound blocking and absorbing materials like auralex. There is this stuff called sheetbloc or something like that and it is supposed to have sound-blocking properties that exceed lead foil (which, by the way is excellent at blocking sound). I haven't tried it because of cost.