Besuchen
The main German word for “to visit”, the act of going to see a person or place, is besuchen.
Ich möchte dich am Wochenende besuchen.
I would like to visit you on/at the weekend.
Ich besuche meine Oma. I’m visiting my grandma.
Note that “besuchen” can also be used in the sense of “to attend”, as in a school or a course.
Besucher
A “visitor” is Besucherin (f.) or Besucher (m.)
Wir hatten letzte Woche viele Besucher*innen.
We had a lot of visitors last weekend.
Besuch
Besichtigen
Specifically for visiting landmarks in order to see them, the verb is besichtigen.
In Berlin kann man viele Sehenswürdigkeiten besichtigen.
In Berlin, one can visit many sights/places of interest.