I made some simple 2D figures but I cannot use the push pull tool in that file
Without sharing the file, or at the very least showing us a screenshot, it will be difficult for anyone to offer meaningful advice.
you might take a lok at square one training videos for tool methods: https://youtu.be/IUVg088Z2OM?si=1n31VEjfJoyVblHN
You probably have hidden/smoothed edges and maybe the faces are not coplanar.