To play soft subs, you need three things: a sub file, a video file (known as a RAW file) and a player that will combine them.
My main source for RAW files at the moment is Nyaa.si (although each page should have a link to the relevant RAW).
Nyaa is a torrent service and in order to download the RAWs from here, you will need torrent software. There are many options, but I use utorrent. When you download from nyaa, tell it to open in the torrent software and that will download the file.
My preferred player is VLC which you can find here.
Before you play the files, make sure the RAW video file and the sub file are in the same folder and have exactly the same name. I always copy and paste from one to the other just to make sure, if there’s so much as a space different, it won’t work.
Then just open the video file with VLC (or other compatible player) and it should play with subs.
If it doesn’t, click Subtitle in the top bar, click Add Subtitle File and then browse to the sub file.
If you still have trouble, click here to contact me and I’ll see if I can help!