There are tons of sites available to explain the process online.
The description to the material you gave is somewhat mixed. CRS is Cold Rolled Steel typically of the ASTM A36 class and 4140 is alloy tool steel. Depending on the form the material was purchased in can change the feeds and speeds drastically.
Here is one site that should help give assistance with the basics of physical properties related to cutting of materials.
Feeds and Speeds concepts
Knowing the exact material is important until you have some experience in seeing what the cutting progress should look like and knowing what to change if something does not. Having a good idea of the SFM ranges for a given material should get you close enough to make those adjustments using the S/F calculators commonly available.