mapping a folder to a user from server

First off, you can only map to one folder deep. For example, you can map to \\servername\foo, but you can't map to \\servername\foo\bar. To do that, you would have to create a share for \foo\bar, and then map to \\servername\sharename.

To map, it's

net use k: \\servername\foldername, or
net use k: \\servername\sharename.

You can use whatever drive you like in place of k:.

To make a permanent mapping, include /persistent:yes at the end of the command.