You must always validate your t+ ticket when you board a bus or tram. Once validated, your t+ ticket allows you to make as many transfers as you want to other bus and tramway lines for 90 minutes (between the first and last validation). Each time you change buses or trams, you must validate your t+ ticket again.
Examples of trips for which only one t+ ticket is necessary:
You take line 62 and then transfer to line 64; you take line 64 and then transfer to tramway T3; you take tramway T3 and then transfer to T2.
Note: the same t+ ticket cannot be used for round-trip travel on the same bus line, or for two trips in the same direction on the same bus line (i.e. you get off a bus and later take another bus on the same bus line).