Who do we call to connect a second location?

Businesses often ask for a site to site connection when what they actually want is for staff at both locations to reach the same files, the same email, and the same phone system. If everything lives in Microsoft 365 or a hosted server, you may not need the sites joined at all, which is cheaper and simpler.

You do need them properly connected when there is a server or line of business application at one site that the other site must reach, when printing or scanning has to cross sites, or when your software vendor requires it.

If you do need it, the usual answer is a site to site VPN between the firewalls, which requires compatible equipment at both ends and enough upload bandwidth at the site hosting the application. Upload is what people forget: a connection advertised as fast is often fast downstream and thin upstream, and your remote site experiences that as everything being slow.

Either way, both locations should be on the same identity, the same security standards, and the same support arrangement, so a user at either site is the same user.