Have you ever seen a photo and wondered what the subject was? Maybe there were a number of things to look at and you could not focus on just one. Sometimes photos can be cluttered with many things and it's hard to find the subject.
In the photo of our dog, Moe, below, I am using the lines of the glider swing (both back and seat) and the lines of the trees to help take your eye to the subject--handsome Moe.
In this photo of our cat, Barney (who apparently went to the same posing school as our Moe), the lines are a little more subtle, using the comings and goings of the rock wall and the pointing fronds of iris plants to help focus your eye on Mr. Hey-Why-Did-You-Just-Have-Me-Neutered. (Longest sentence ever.....so glad someone invented commas.) I used a 70-300mm lens at about 105mm for this shot because Barney is avoiding me just a little since I put him in that cat carrier to go to the vet.