Poder and haver de take an infinitive: puc venir, he d'anar-hi. Caldre is impersonal - cal + infinitive means "one must", and no cal means "there's no need". Note that haver de keeps the de: he de trucar, never he trucar.
Examples
- Em pots enviar l'adreça?
- Can you send me the address?
- Avui he de marxar més aviat.
- Today I have to leave earlier.
- No cal que hi tornis avui.
- There's no need for you to go back today.
The mistake to avoid
Haver de is obligation; tenir que is a Castilianism that Catalan style guides reject even though you will hear it.
Where this fits in
Telèfon, missatges i petits problemes, Catalan A2: Trucar i escriure, demanar disculpes, aclarir un malentès i demanar ajuda - el dia a dia quan alguna cosa no va com estava previst.