How to select BitCoin address for receiving money?

[DireWolfM14]

As others have already mentioned, "receiving" (green) addresses and "Change" (yellow) addresses function the same from an external point of view.  If you are receiving bitcoin from a sender, you'll receive it regardless of which type of address you supply to that individual.  The only difference is how the internal function of the wallet selects the addresses.

Since Electrum wants to reserve change addresses for change, it's best not to request payments to those addresses.  The use of empty addresses can help you keep track of your income and spending as well.  If, for example you receive regular payments from one individual, you may want those payments (and only those payments) going to a specific address so you can keep good records of those payments.

The way you use receiving and change addresses can have privacy implications: If you want to maintain privacy it's best that you don't mix coins from separate receiving and change addresses.  Using the "coins" tab you can select specific transactions to combine to avoid cross-linking unspent coins.

Testnet is a practical way of learning how Electrum behaves.  You may want to create a testnet wallet, and fund it from one of the many testnet faucets.  You can then create another testnet wallet and send the coins back and forth between the two.