just use the inlets for the loop start and end points. You can use sfinfo~ when you load the file in at first to get the total length in ms. The same button to load a file can get the info and fill the buffer~. then it's all about groove~.
you might want to check out some ways of using a line editor or some other function to create a rfast amp down and up at the endpoints to avoid clicks. There's a lot of ways to do this relatively essential element of loop playing. Check out sequencing-looping in the examples folder, plus lots of posts on this forum address it.