A language exchange involves pairing a visiting student who is learning Catalan with a Catalan-speaking student who wants to practice another language. Most Catalan universities have a language exchange register that they use to put students in contact with each other based on the languages they want to practice. From this point on, the students themselves arrange their meetings.
If you are not a university student you can take part in the Language volunteer programme, organised by the Language Policy Secretariat, as a learner.