Your game should automatically save your replays and best lap during Practice, Qualy, and the races.
They can be found in C:\Steam\SteamApps\your user name\race 07\REPLAYDATA
The location may very depending on where you installed the game.
To view them, just go to the replay menu, select the one you want and hit play.
To download and install a replay file, unzip it, and place the .vcr file into the above location and play it the same way.
I hope this is clear but if not ask again.