Subdivision Surface

I worked on some stuff,and i noticed that the Subdivision Surface Modifier always makes such waves.

I recently watched a tutorial where somebody was modeling,and his mesh was perfectly round.
I my case,Subdivision Surface always makes that waves on round objects such as Spheres and Cylinders
Any help would be nice

Change the end to all quad faces. You’ll get this with triangles (or ngons which will act as triangles).
You’ll see the same effect at the poles of the default sphere which again are triangles. You may get away with triangles on planar surfaces

Select the end face, and hit i for insert; that will allow you to add some loops easily. It’s a great way of adding loops to ngons. Select two verts and hit j to add an edge between them.

Shade smooth if u havn’t (w key); You may need yo recalculate normals (ctrl n) w then select recalculate or flip when recalculating doesnt help.