Best is EOS Authority's portal:
They have a video as well:
The architecture of the contract is so that you cannot lose your initial input unless the contract is somehow hacked. When you stake to REX your balance will lower in blocks for your staked CPU amount. You receive REX ...
Probably the best tutorial is to take a look at the Universal Authenticator Library - UAL and how it works.
Here are some helpful links:
Medium Article about the UAL
UAL Authenticator Walkthrough
There are are several different UAL-Repositories + Usage-Examples for use with the different available Wallets.