Firewall? What's that?
In cyber security, a firewall is a network device (either hardware or software) that helps to keep the bad stuff out of your network.
A firewall is your first line of defence. You can use it to allow, or more importantly deny connections into and/or out of your network.
In most small businesses, same as at home, your firewall will be an integral part of your router - which in most offices/homes is your WiFi router. It is worth checking to see what settings you have in there, and what you can do.
Block inbound connections unless you have good reason to allow them.
In most networking environments, you rarely need to connect from outside of the office (or home) in. Unless you know that you need to allow an inbound connection, (for example, to a server, cctv etc), then you can block them all. This can help to prevent hackers from getting into your network in the first place.
Outbound connections are rather harder to manage, and frankly in most network settings outbound connections are ignored - and explaining what/why you might block outbound connections is a little too complex for this article!