I encourage you to watch all three videos, the first will allow you to easily place the grass, the second has a pretty great texturing section, and the third is a full workflow for a more complicated scene, using what you learned from the Beginner section. If you make grass using the beginner Video, texturing the grass using the second video, and making and texturing the ground from the advanced one, you will have mastered making grass scenes in blender. Next how to animate them.
This is the new geometry nodes method. You can still use weight paints to place the grass, which he doesn't mention.
(Particle system Version) He makes a grass object and textures it. His setup of the grass uses transparency and translucent. Most importantly he uses the object info node's random value to randomize the colors of the instances of the grass. (using a color ramp with different colors he chooses for the instances) he then uses a mix node to connect that to the color in the principle shader. He makes a vertex map and He uses a weight map to place the grass. (non geometry nodes version) He then uses particles to place the grass on the plane. You can use the wind effector to animate the particles.
He uses a built in plugin to generate the landscape, adds in an hdri image for the background lighting, uses the a.n.t lanscape plugin with the mesa preset, uses the plane and textures with a noise for the bumpy waves, he then textures the land with a rock texture,(resets the uv) and then makes a grass object, he then opens a geometry node window, and adds a point distribute node, he selects the ground object, and makes a vertex group (v1), he then draws on the vertex group around the river,* weight map mode) adds 2 attribute randomize nodes (remember to set to vector and only change the z), and a point instance and selects his grass object, He then clones this geometry nodes for the grass setup, and makes a new weight map. (v2) and paints a second weight map along the edge of the water, he then adds a multiply and value node to make the density higher. (why though) he then takes the value from the multiply node and adds that as a pass through to the (input) of the geometry node group allowing a density value to easily be shown, on the side.