I've just got to the point where i can use robots. How do you go about ghost building stuff? Do you have to use blueprints? Can the constrution robots just build anything for you if the mats are in chests?
You can just place ghost items by hand (press shift) but not much point. The advantage is being able to smack down whole bunches of machines in blueprints.
They can build anything if the products are in provider chests. They have the exact items, they won't build from intermediate materials.
You can also start a Sandbox game mode to explore everything you can do (note infinity chests are extremely useful, you pick a item in the game, and it will produce as many of them as you want perpetually, then your inserters can pull those out into conveyors simulating different parts of what you'd like your factory to look like). Definitely recommend this approach, you can explore as much as you'd like to explore.
Also note, there are a few websites with prebuilt blueprints as well.
Edit: fixed a typo
There are tons of designs you can do with bots, some have built completely belt-less bases using them. They're limited by their speed and range however, so you always have to balance to the constraints of the tools you use.
It takes a lot of the tedium away when you made a miscalculation and need to be just a little bit closer or further from something.
Now you can cut, move over 1 and paste.
I've also found it really nice for rails. If you want a t-junction, just go away from everything and make a 90-degree rail curve. Then cut it.
Then go back to where you wanted the t-junction and paste in the curve and rotate it and paste again to get perfectly lined up sections of track.
and then you can have blueprints and upgrade planners and destruction planners.
upgrade planners let you convert say all slow belts to fast belts and leave the inserters alone.
destruction planners let you remove only walls but leave the electrical towers and rails alone.
it just goes deeper and deeper.