How do you restore the browser if lost?

Often you'll automatically be asked if you wanted to restore your previous browser conditions, but if not do the following.

Click on the sidebar of your browser after reopening it. Hover over the history section. Under "recently closed", you should see the number of tabs you lost. Click them, and they will reopen.

You mean your tabs? In Chrome and Firefox just press Control, Shift, T and it will open the last tab you closed.