Hi and welcome to the forum. The AE-1 has two focussing aids when you are looking through the viewfinder.

One is a split image rangefinder, this is the central circle where the image is split into two halves. Correct focus is achieved when the two halves match up, when out of focus th image is offset slightly in the upper and lower halves. With longer lenses this central area or one half can become darkened.

The other is a microprism ring. This is the circle outside the central circle and will appear clear when in focus and will look like lots of small triangles when the subject is out of focus.

Hope this helps.