Goto the file menu and open document and then view menu and show grid.
It can be used for create objects and snapping to a predefined object. You can use it with images and then use that image to create a sketch / drawing / painting. You can use them to align text and objects and much more.
View menu and show command and it will then hide it
You can find it View menu and Grid and axis manager.
The default, not a favourite but if you want to set up something quick then it is fine. You do have control over the grid lines and subdivision lines color and the opacity for both and that is it. You have the main lines and then you have the slightly faded sub divisions, you may like four or five of those or just not use them at all. I always find them more confusing and often either change the color totally or fade them or just leave it as none.
More useful as you can then set the spacing to something other than 64px, say to 100px or 200px etc or 1920/10 (you can do basic maths in the edit fields so 5 x 20 etc. You can also add in some finer lines via the subdivisions (though the edit field is called divisions, if you want none, leave it at 1 (which is confusing).
If you move from basic to advanced tab, nothing changes other than everything is moved to the first axis entry and you now have the option for a second axis as well as up axis but they are only available depending on the type selected, the default one is 'standard' (shouldn't that be basic). There are many different types to choose from such as isometric, diametric etc and they are easier to show in action in a video.
If you don't want the basic, you can deselect the uniform and then you can access the second axis and enter different spacing, divisions, gutter etc from the first axis.
If you select an angled type then you will see the angle entries change though you can't access it directly in many cases. If you go to the 'two axis custom' then can alter the angle fields directly and also with standard deselected, you can angle the entire two axis design (my favorite).
You can also add in a gutter. That two lines where there was one previously and it will be separated by the gutter amount and that is repeat for all the lines. You can add a gutter for both axis and they can be independent. The gutter is not applied to the sub divisions.
If you create an amazing setup then you can save it and that is done via the top of the panel, presets. The menu at the side of the presets allows you to add this set as a new preset and you can also manage the presets (delete etc)
If you change a type, be aware that the settings such as gutter etc setup for the previous type are lost as that type may not use gutters (though why gutter isn't available in all of them is baffling). All the types use the same axis but in some cases the settings will be fixed and non-editable such as triangular where only one axis is used but set it in one and all will be updated accordingly.
Set that on and you will then be able to enter a different value from 1 in the aspect ratio field, such as 0..5 or 0.3.
Once you have added it, you can also use the snapping features. View menu and snapping manager and make certain it is on. You can snap to the structure you have just created, so paths will then snap to the cells etc
You can go to the manager and go tot the basic section and set it to a third of the document / width and third of document / height so if it is a 1000 then enter 1000 / 3. However, if the document is 1920 x 1600 then you will have to go to advanced and deselect uniform and enter 1920 / 3 in one axis and 1600 / 3 in the other. Another solution is to show guides and use guides instead and set to 3 and 3 and set to outline Youtube video on subject