An address (a.k.a. bitcoin address if talking about bitcoin) is an identifier for where cryptoassets can be transferred to or from. They are generally 26-35, and are mix of numbers and letters, but it depends on each different cryptoasset.

For example, a bitcoin address held by me is 1BeTaAhBPQKMD5QpgHK1g5DB5oUevCotcs. If you send BTC to this address, I will receive it. And I'll be very happy and appreciative 🤗

The only harm in sharing your bitcoin address is you lose privacy when it comes to the crypto stored at that address. For example, if a lot of people sent me BTC to that address, and I've shared it on this site, anyone could go to a public blockchain viewer and see how much BTC has been sent to it. They could also see how much I've transferred away from it.

People will not be able to take from that address unless they have your private key (your password to your address). Which if you're using a secure wallet app, or hardware wallet, is basically impossible.

It's like sharing your email address, except it's very likely that your private key is a lot harder to crack than your password.