How can I protect my privacy?
The simplest way is to not reuse addresses, something that wallets do by default anyways. Every time you want to receive Bitcoin, get a new address from your wallet and give that to whoever is sending you Bitcoin. You typically do this by going to the "Receive" page or tab in your wallet and clicking "Receive Bitcoin" (or similar). By doing so, the sender will not know how much money you have in your wallet and they won't be able to see all of your transactions.

When you send Bitcoin, you should also use new change addresses every time. This is the default behavior in wallets so this is not something you need to do manually or worry about.

By not reusing addresses, it is harder to link your transactions to you and it makes it more difficult for everyone you transact with (both receive and send) to know how much money you have and who you are sending money to or receiving money from.