The infinitive of every non-reflexive Latvian verb ends in -t.
The infinitive of every reflexive Latvian verb ends in -ties.
So you could also say that to make a verb’s infinitive form reflexive, you just add -ies to the infinitive.
What is an infinitive?
One of my professors liked to say that the infinitive form is the “dictionary form” because it is the form you would look up in the dictionary when translating into English.
It is the basic form of the verb used to construct all of the other verbal forms and is translated with “to” prepended when being used as a “full infinitive.”
You can read a lot more about infinitives at Wikipedia, but technical grammar is not my strong point so I’m going to stop here. When you translate into English, you’ll pretty automatically know whether or not to leave the “to” on or off because it will either make sense and sound right or it won’t.