You get the basic details from an online will index first. Then look at the will links on RootsChat:-
Click on each of the will links and each will take you to a FS page of wills. Look for example for film number 106508. Once you find it if it has a camera icon next to it then you can view it. If it doesn't it's not available to view.
Sometimes the will index will have a reference that makes it easier to find. I find the earlier wills more difficult than the later ones. The will for John Kelly of Lonan was numbered 67. I went through the film in 50s and 100s looking for numbers on the way. Once you get the idea of how the wills are set out you can move more quickly through them.
Top left is an image page number click on that and change the page number and click enter/return. The image will reload and show you the image you just selected. Use + and - to maximise and minimise the image. You can use minimise to view many images at once to get an overview of what is on the film.