I noticed when I render my low poly tree I get this weird shadows/almost unfinished rendering. The render looks all pixelated. What i'm I doing wrong, i'm a complete beginner. thanks! Also i'm using filmic blender.
You haven't rendered anything yet. That's just cycles render preview which uses less samples. You can increase the samples in the render properties. Pressing 'F12' with a camera object in your scene will use the default 128 samples and look much better. The noise in your image is considered normal for the settings.