Midi files can be a great way to practise your part. However, you cannot just play them in a browser – you have to download them first and play them using a suitable application. The key thing to remember is that they only contain instructions to play the music, and the quality of the sound depends on the sound samples used by the application. So a midi file is a bit like printed music where the quality of the sound depends on the performers.
You can play the files below in some basic applications such as Windows Media Player on a PC, although sometimes it doesn’t cooperate. Ideally you need to find something where you can have some control over the tempo and even be able to adjust the levels of each channel (such as your part). Sweet Midi Player is recommended but it isn’t free. It is available for PC and Mac (~£20), iPhone and iPad (~£10). You are best off with a computer connected to a pair of speakers.
There are lots of websites where you can find out more about midi files, but here is one suggestion: http://www.learnchoralmusic.co.uk/index2.html#introduction
This website also contains a huge selection of midi files for learning choral parts. Clicking on each link will take you to the appropriate page from where you can download the files for your part. Simply click on the symbols in the tables.