Memo/Tag/Message/ is a combination of numbers and letters required to transfer XLM, XRP, EOS, NEM, ATOM to a specific XLM, XRP, EOS, NEM, ATOM wallet user. If the recipient of the transfer requires you to specify a Tag/MEMO, you must specify it, otherwise your transfer may be lost.
The /MEMO/message/Tag is an additional note to the address needed to identify the recipient of the transaction in addition to the wallet address.
For coins like XLM, XRP, EOS, NEM, ATOM, most centralized exchanges use one address for all traders. Thus, Tag/MEMO/message is used to determine to which actual individual account a given transaction should be assigned and credited.
Example: the address to which you send one of these cryptocurrencies can be equated to the address of an apartment building. The /MEMO/message/Tag defines which specific apartment you live in in this apartment building.
YOUR wallet can be without a tag, then FOR RECEIVING leave the field empty.
When SENDING us TO OUR details, both the TAG/MEMO and the address are required to successfully deposit coins into our account.