How do I add some custom 1.13.2 plant and grass blocks

first off I just created this account for this question and don't know if this is the right forum.

I started making a mod for 1.13.2 but I want to add stuff like custom grass (not the block the actual plant) grass blocks (to place grass on my grass and custom grass) and I might also add flowers later on I don't know what block properties I have to use (I only started to make the grass blocks)