Autocad requires being able to conceptualize a 3 dimentional space in only 2 dimentions (the screen remember is flat) so therefore the most difficult part will be rotating around the various axiis of x,y & z. this is difficult because your frame of reference (think of a camera here) is what you see so therefore you fix your reference at where you're looking and spin in 3 directions from there. There is actually very little difference between "Autocad" and some other softwares available with cad lite programs being downloadable as a demo and trialware which will give you a chance to play with them. This is because the concepts are the same. Autocad however is going to be one of the most recognized and has the most plugins but you can draw with other programs with little training once you know one.
There are classes available at the community college level for cad drafting. It helps but is not required that you know drafting because the concepts above are the same... seeing things in 3d and converting them to on-paper in 2d.
Also, once you get used to the concept of 3d drawing, then you just need to get a handle on scale (drawing items in a scale in which it is going to be true to your design) since it is easy to get things out of proportion (you're pretty much freehand drawing here) make sure you set your scale to 1"=1' or something similar or always specify the distance of your target. Finally the most difficult - kidding. It's actually the easy part of autocad is rendering what you've drawn (it takes forever but if you draw it right you should not have any problem and rendering requires that you have the lines of objects be represented as actual objects with color, shape and size) to create a 3d picture of the final product. if you do enough of it (autocad) the process becomes quite routine. keep in mind that many projects (even simple ones) can take hours to build when you first start. I recommend for starters creating a picture frame in autocad (no rounded lines or corners to worry about) with the 45 deg angles on each side that come together with a light wooden backing with a spot for a picture to slide into from above. this would be a good practice. once we get that down, move to something a bit more advanced. try and draw a tricycle (lots of rounded corners and circular tires. Then you can move up to drawing rooms. When you draw rooms, you will draw them in layers. This is done to minimize the possibility of forgetting something. There is the electrical (wiring), plumbing, ventilation and building layers with the final layer being furniture or stuff actually in the room (yes... you can put in plants, chairs and other things in your autocad drawing) when you combine the layers, you'll need to check that none overlap (no sense in sending the wiring THROUGH the plumbing pipes) and then you need to ensure it's up to code. check that the spacing for supports is 16" oc for load bearing walls or that electrical outlets are 12" from floor and other code like that which will often be overlooked by the engineer (since it's not affecting the heath of the structure). also it's important to remember which way and how wide a door is so that it swings (or slides) in the right direction with proper clearance. If you can build a room... you can build a house. If you can build a house with a few rooms, You can build a building with many rooms.
The important details can often be left to the engineering group for placing or recommending where load bearing walls will be or how many supports in a building will need to be where and how often. You're just starting. Don't try and tackle everything at once.
It is the planner's design to work around the physical requirements to support the structure how the internal layout is organized. Where the staircases are and what the lighting is like, what the kitchen is if it has an island, a hallway, a skylight etc.