It depends on what kind of tree your wanting to make a (pine tree, or a tal tree). This could done by using different mesh selections usually a pine tree is created with a cone and cylinder while the trees that have branches or more created, through using a plane and placing a modifier into it (skin). It’ll fill the tree and you could resize the tree to your own liking.
Since your more of a beginner and wanting to learn the blender and the ropes and curves. I would recommend blender gurus beginner tutorial (donut & mug one) is a great place to start, it’s decent in terms of learning the basic tools, techniques, and workflow around blender. He also goes into details and explains everything you could always take notes.
You could even use the blender forum for asking questions and wanting to learn the process or for having issues on different things your stuck on. Here is a thread that has useful information that I would recommend taking along the process: