Hi,
I ve rb2100 with routeros 6.20 and i would like how can i connect a usb printer to the microusb port of rb2100 for setup a network printer. Thanks.

This is impossible because the routerboard has no print-server onboard.

How can I do???

Not

I ve rb2100

What is rb2100?

how can i connect a usb printer

Not sure, but you can try metarouter+OpenWRT
http://wiki.mikrotik.com/wiki/Manual:Metarouter

Routerboard 2100...