Levels, Offset and Adhesion are the three most common words in the world of 3D printing. As a beginner they confuse and frustrate you. Then once you are a master or competent they will continue to surprise you.
Check your foundations.
Use the ruler measures on the Z Uprights (if available) and/or get a small spirit level and check that the bed is level to the eye. This is going to save you time later on. Is it level left to right and front to back. Does everything feel stable. If you need to place a soft mat under the printer to stop any movement – do this.
Level the Bed
If you are levelling the printer out of the box you will probably need to back off the dials 1-2 complete turns each so you have some adjustment in both directions.
The Ender (Plus) provides a built in Bed Levelling Feature which moves to five points on the bed. The user then tests each corner with paper (0.1mm) and adjusts the corner screws/springs to bring the bed level. Creality suggest doing this a few times as each time you bring the bed closer to level.
At this point I would mark the most forward facing groove of each dial with a white tick so I have a reference point to how much the wheel has moved.
Without the feature above (or in addition) you can use Pronterface, G29 Marlin Command and a bit of spreadsheet action to get a mental image of the bed level. If you connect the printer to Pronterface (other Slicers provide the same features) you can send G28 (Autohome) followed by G29 (Auto Level) to get a grid that can be copied/pasted into a Spreadsheet.
Once you have pasted them into your spreadsheet software you can analyse them using a mixture of conditional formatting with max, min formulas subtracted to give range. I complete it eight times because that what fits on my laptop screen.
The Ender now reports the auto level mesh as:
Setting the Offset
At this point you need to set the Z Offset between the nozzle and the BL Touch. The manual for my Ender+ says a 0.2 feeler but this was too high for me so the faithful UK Lotto slip (0.1mm) was brought back into action. Adjust Z+ / Z- and then once you are happy press Z Home.
Flip the glass!
Lots of manufacturers provide funky non-stick textured surfaces on their printer beds. A mooch around the forums quickly informs the observant that these are often a cause of problems.
My advice is flip it over to a smooth glass side or grab a piece of mirror and use a splash of 3DLac to help adhesion. Mirrors are ideal as they will be flat unless its one you have borrowed from a hall of mirrors maze!