Your computer will downloaded to a folder called downloads or you can click 'save as' and put it into C:\User\junxian32\sports interactive\football manager 12\tactics. If it goes into dowloads - copy it and paste it in C:\User\junxian32\sports interactive\football manager 12\tactics.
Go into tactics page on your game, click on add a tactic, click use a saved tactic (I think it says that) and then choose archived tactic.