At the menu bar, go to "Tools", then "Network" and set:
Proxy: SOCKS5 | 127.0.0.1 | 9150

This should work with the recent Torbrowser (start Tor before you start Electrum and quit Tor after quitting Electrum).

Undoing the whole thing:
Menu bar "Tools", then "Network":
Proxy: NONE

If you really don't know the advantages, you probably shouldn't use Tor.