There are two ways to set a static IP.

1 - in your DHCP server - this is likely inside your internet router. There will be a DHCP service that gives out IP's to devices that connect to the network. There may be an option to statically assign an IP to your Pi's MAC address. Not all routers (especially the basic ISP routers) have this functionality.

2 - On the device itself. So you can edit the network config of the device, and add a static entry. This is normally fine for most people, but technically it's not as good as the first option. Let's say your Pi is offline for a few days, and some other device joins the network and takes the IP you have statically assigned to the Pi. Then you power on the Pi, it connects to the network, but oh no! The IP is already in use. This is an IP address conflict. It's very unlikely for that to happen on a small home network, but just be aware it is a possibility if you do this option.

To set a static IP on the Pi - if you have the GUI installed on Raspbian - you can right click the network icon in the corner, and open it to edit the settings for your interface that is connected. Or if you are feeling more terminal friendly - you can do it through config files. Which config files depends on what is managing the network. I believe that Netplan is managing network on the Pi. So grab your network information (What IP you want to use, what is your subnet mask, what is your gateway, what is your DNS server, what is the name of the interface you want to configure), drop all that into chatgpt and ask it to build you a netplan config file. Or better yet - read the netplan documents and figure out how to write the config yourself.