By Metro and train
There is a manned barrier and automatic barriers for those with cards at almost all of the stations.
At the smaller country stations there might be no barriers at all. You must have credit (reskassa) on your SL Access card, buy a ticket with the app or text-me-a-ticket services, or buy a single use travelcard in advance.
All Metro and commuter trains stop at all stations along the line, apart from express trains that skip certain stations. Express trains only run on the commuter rail lines and during peak hours.