Some auxiliary verbs cannot be followed by a bare infinitive: we need to place the preposition te before the infinitive.
In English, we have the same phenomenon. We say "I want to sing" not "I want sing". On the other hand, we do not say "I can to sing" because 'can' is normally followed by a bare infinitive.
When you go through the next pages, you will find that Dutch and English are quite similar.
If you do not feel like reading about all the different instances of infinitive + te, you can also scroll through the list of te-verbs.
All in all, there are six situations where we use te + infinitive:
: "Ze proberen (om) te vliegen."