If you setup a dual-boot, make sure that you install os-prober.
Generally searching for "Software" or "Program" on the Beginner Distros will pull up a nice interface for you to search for and install packages. For more see here.
In general, search for "Update". Some distros have a nice interface for updates. If not, see here.
With Windows you needed an Anti-Virus program, but not in Linux. (see here if you want one anyway). However, it is recommended that you have a firewall to block other computers on the network from making connections into your machine.
To set up a firewall:
Install the package gufw.
Click on the status slider to turn it on.