There is small ISP at my client office building.. that ISP use MikroTik DHCP Server & hotspot feature..
So, if i want to connect to internet from PC/Laptop, turn on the wireless, obtain the IP from DHCP Server, and then need to open browser for enter username & login.

Well, i need to share the internet.. i'm planning to use MikroTik board..
MikroTik (ISP) <-----> MikroTik (my client's office) ----> LAN

I wonder how to connect/login to ISP hotspot from my MikroTik?

thanks,
Yudi

anyone? please

I don't think you can use RouterOS to log into a hotspot as it cannot do HTTP POSTs. It also rather possibly would violate the ISP's terms of service to share the connection. Contact the ISP for options.