Keep these points in mind about Memos and tags:
1) The XRP Ledger allows receiving accounts to enable a “destination tag required” setting. When enabled, transfers without a tag will be rejected.
2) To make account management easier, many exchanges let multiple users share the same deposit address, then use a Memo or Tag to identify who each transaction belongs to.
3) The first time you deposit to an address that requires a Memo, you can try a small amount first to see whether it arrives.
When depositing $XRP to an exchange, you generally need to enter both the address and the destination tag (Tag).