Much of the learning about CNC Milling will come from chewing up a lot of board stock. Start 1st with the many You Tube Vidoes as most will explain the fundamentals. But this is much like ham radio -- you go from 5 WPM in CW to 25 WPM only by regular and routine practice.

But there are some fundamental Tips to Success.

1. Sart with small project where the outcomes are easier to manage.
2. The key factors in any machining process is Speeds and Feeds. Speed in this context refers to the Spindle Speed (not too fast and not super slow); whereas feeds refers to how fast the part is moving under the spindle.
3. Tooling to secure the parts to the bed of the machine. Using Double Backed Tape is not acceptable. Real tooling to clamp the parts to the bed if you want accurate professional looking boards. Tooling is typically sold as accessory items. Don't chintz on the tooling.
4. Sacrifice boards! Typical board making entails cutting just the top surface of the board and not a clear through cutting. But at times you will cut all the way through a board and it is just such a situation you need to install a sacrifice board between the PC Board and the bed of the mill. Thus when you cut through you are not damaging the Mill bed. Typical baords are 1/8 inch hobby plywood that would cover the area under the part. Thus a cut trhough cuts the plywood and not the bed.
5. Shop vacuum. Get a shop vacuum to vacuum the dust created during the milling process. When emptying the vacuum use the KN-95 mask and your gloves