The metro in Stockholm is a great service that is really easy to navigate. I will be honest, after I got off the flight I tried to get the overground train which would have got me to rural Sweden instead of the city centre. I went to one of the very lovely station workers and had to get pointed in the direction of the metro. Once you get pointed in the right direction it is really easy to get around! I have done a post on whats the best things to buy to get around Stockholm, check it out here.
Along the central line you can find gorgeous artworks in the tbana stations. Here are just a few!