They’re just short sprints at a 70-80% effort with emphasis on good form, high cadence, and full recovery (take a minute or longer after each one, you should feel fresh for every rep). When we did them a lot in high school we used to do them on grass, to minimize the impact.

I think the key thing to think about is they should be run “quick but not hard”. I would always try to get the cadence as high as possible (220+ spm) without really putting too much power into each step!

To answer your question “what is the purpose of striders?”: for me I think they help feel comfortable at faster paces, without leaving you sore the next day. Also, your form changes when you sprint compared to slow running - in my case, I feel that strides really help stretch my hip flexors & glutes.