Simply just hit an endpoint with yours SA:MP server IP and port (if it is not 7777).
https://samp-api.tk/server/{yours server ip here}{:port}
E.g. https://samp-api.tk/server/127.0.0.1:7778
You can also use domains https://samp-api.tk/server/play.domain.com:7776
If server uses port 7777, you don't have to put it in request https://samp-api.tk/server/127.0.0.1
Else if it uses other port remember to put :
between ip and port
You still don't know how to use it? Scroll down to the bottom of the page (to test section) and type your ip. You will get a response and a link.
Response will show up here