back and forth

"Back and forth" is a common phrase which describes something that goes in two directions. You can use "back and forth" to talk about traveling:

They have an apartment in London and a house in Boston, and just travel back and forth between them every few weeks.

You can also talk about something that swings or sways:

I'm just sitting here, watching the bamboo sway back and forth in the breeze.

switch between (two things)

"Switching" means to make a quick change from one thing to another. For example, if you're doing some difficult work with one hand and start to get tired, you might "switch" to the other hand.

You can talk about "switching from ___ to ___":

I'm thinking about switching from my iPhone to an Android phone.

Or you can use the phrase "switch between":

How do you switch between different accounts?

"Switching back and forth between" things means switching many times between the same two things.

tabs and windows

On a computer, applications have "windows". A window is a box that you can put in different places on your screen. Some applications allow you to open multiple windows.

Inside of a window, you can have different tabs. Tabs are little handles that usually sit at the top of the window. When you click a tab, the view switches to show that tab's contents.

Hit Command-T to open a new tab, or Command-N to open a new window.