The trams in Bern are excellent and you should use them often. The nice thing is as a tourist they will be free to you! When we first arrived I had read that this would be the case so I confirmed at the train station TI, your hotel reservation is what you need for your initial trip to your hotel. After that your innkeepers will give you a small card that lets you ride for free for your entire stay.
In case you are the type who likes to live life on the edge, the trams work on the honor system. That is, you are supposed to buy the ticket and have it on you, but you don't show it to the driver and there is no conductor. Obviously they do spot checks, but over many rides over several days we were asked about tickets exactly never. But don't chance it, I'm sure they make the fine high enough to cancel out any savings you may have.
Pick up a good tram map (at the TI) they made it look like the London tube map. Since many lines run parallel or on the same tracks, figure out which ones stop where you need and which don't. The TI gave me some bad info but by looking at the map I realized we had chosen the wrong number line so got off and waited for another. Each stop has a ticket machine and also a sign indicating how long until the next tram and what number it is.
Be aware that the trams not only have the right of way, they are silent and will not make any kind of noise if you are in the way to remind you to get the hell out of the way. Never saw that before. Wife had to pull me to safety several times. I'm used to bell being clanged or a horn blown.