Support is a structure that it’s not part of the 3D model, still, it sustains the entity or some parts of it; most of the time, it is necessary for overhangs bigger than 60°.
In Cura, supports are light blue colored, and at the end of the print, you need to remove them.
The contact between the support and the 3D object almost always shows during the removal process, that’s the reason why you can leave some space in-between. It’s primarily used for aesthetic looks.
On the other side, if looks don’t matter, be careful to match them well.
You can reduce/modify the number of supports and their density, following what the forms of the 3D model are.
Touching build plate: supports don’t grow where there is no contact with the platform.
You can change the structure type of the supports, the overhang angle, the fill amount, and the X/Y/Z distance.
If you’ve just started with 3D printing, I suggest you set 65° as an overhang angle.
Here you can see what means changing the overhang angle support:
45° 
65°
Setting the supports is based on what are your needs, for example, if you need your 3D entity to be esthetically pleasant or if you just need it to be strong and functional.
My suggestion is to use lines. Grids are for objects you want to detach in one-go.
Fill amount (%) changes the distance between the lines of the supports. I usually set it from 10 to 50%, according to what are my needs at the moment.
Changing the distance on the X/Y-axis is important where you need a smooth surface. The bigger that distance is, the farther the supports will be from the X/Y-axis.
The farther your supports are, the easier their removal will be.
