@captain How to these 3d printers work ie if you have a part you want to replicate do you just scan it or what?
There are various ways to use them.
You can visit various websites that have lots of parts & things already sorted for 3d printing, these can range from small parts like cogs, knobs etc.. to huge jobs like a fully working and fully 3d prinable wall clock (even the spring it 3d printed).
If your CAD skills are ok then you can download various FREE CAD programs to design your "part" and then save the file ready for slicing and 3d printing.
If your CAD skills are not up to much then there are various websites where you can request someone design something for you but that costs, obviously. There are a ton of tutorials on youtube for CAD software like Fusion 360 (it's free for personal use too).
You can scan an object (the British Museum has scanned many artifacts and placed them on thingiverse for downloading & 3d printing) with one of the available 3d scanners or apps on your mobile (using the camera). The results range from really crap to really detailed (as in the British Museum scans).
Personally I have not scanned anything but I have used CAD software to make my own phone/tablet docks and various boxes and holders for things. Used thingiverse for many projects like various attachments for the Dyson vac, wall mounts for guitars, stands for things like Alexa Dotty etc...
Plus many upgrades to the 3d printer itself and many, many little trinkets and dust magnets.
It's not as expensive as it used to be ether. The Anet A8 (classed as one of the best 3d printers you can buy in kit form) is only £130 on Gearbest (as 11th may) and filament can be had as cheap as around £13 for a kilo spool.
I subscribe to Maker Box which gives me several filament samples per month, it's not too cheap at £40 bi-monthly for 8 samples of around 16m each but it's a good way of trying exotic filaments without the need of paying £60-£80 for a kilo spool.