to put something inside an envelope as well as a letter:
Please enclose a cheque with your order.
please find enclosed (=used in business letters to say that you are sending something with a letter)
Please find enclosed an agenda for the meeting.
2 [usually passive]TBC
to surround something, especially with a fence or wall, in order to make it separate:
The pool area is enclosed by a six-foot wall.
an enclosed area