If you intend to keep it, it is imparative that you know what species it is, as a garter snake will have a very different diet from a rough or smooth green snake (both of which may be "olive green"). I wouold recomend either looking it up in a field guide (or the web), or posting a pic here so someone can ID it for you.
If you don't intend to keep it, and you don't want to run the risk of it getting back into your house, then the next best thing would be to take it to a wooded area a few miles away, and release it there.
Normally it's always best to release a snake where you found it, but in some cases it may be necessary to release it in a similar habitat to that of your yard but far from the presence of people, so that it doesn't run the potentially fatal (for the snake) risk of running into people again. Some peoiple may not be as kind as you are if this snake crosses their path.