I'm not an IT guru but I've done this before for my own business with multiple offices in different cities. You need a VPN (virtual private network) between both sites. Think of a VPN like a secure tunnel through the internet. A VPN will allow remote computers to act like they are on the same network. Then decide if you want to host your own servers or contract this out to a 3rd party. This means will your database be located on a server physically located in 1 of your offices or will it be located off site in a data centre somewhere. If the IT requirements are simple then it might be more cost effective for you to host your own server/'s. If it's a complicated set-up then 3rd party hosting will probably be the better option for you. Also a lot depends on your budget. In all honesty this is the point that you probably need to pay a consultant to plan & manage the process for you, that's what I did.
I just saw my parents having sex, that's the last time I visit that website.