There are two different concepts at play here: validation, and tickets.
You have to validate:
- Any time you enter the metro network (by going through a turnstile)
- Any time you enter or exit the RER network (ditto)
- Any time you board a bus or tram (by using the validators near the doors).
A t+ ticket is valid for a single trip across either the metro + RER network (metro currently anywhere, RER inside Zone 1, aka the actual city of Paris), OR across the bus + tram network. There are time limits in each case (counted differently).
Each time you validate, either a new t+ ticket is used (if this is a new trip, or if you switched networks), or the current active ticket is automatically re-used if it’s still valid and you didn’t switch networks.
In your screenshot:
first itinerary (line 1 then line 7): you validate when you enter the metro station, it will use a single t+ ticket. No further validation.
second itinerary (line 1 then bus 47): validation when entering the line 1 metro station, then when you board the bus. Two tickets will be used.
third itinerary (line 1 then RER B): you validate when you enter the line 1 metro station, then when you go from line 1 to RER B, then when you exit RER B, but it will all be on a single t+ ticket.
Note that metro-metro and metro-RER connections must be made within the same station complex, or via one of the approved out-of-station connections.