Howdy. In Preferences, go to International (top line of apps), then click on the Input Menu (3rd tab). Scroll through the list and check the languages you want (including English). Then at the bottom, check the box where it says “Show input menu in the menu Bar”. Click OK. You should see an American flag (if in US) in the menu bar on the right.
Now when you work in an application, you can use shortcuts to access those languages you checked.
CTRL + Option + Command + Spacebar will cycle through the languages (watch the menu bar for the symbol to change). If you use two more frequently, you can use CTRL + Command + Spacebar to alternate between the two.