Getting Started

A 30 minute overview of many common 3D printing concepts and techniques: 3D PRINTING 101: The ULTIMATE Beginner’s Guide
An excellent playlist that goes into more detail about core 3D printing concepts: 3D Printing Basics! (Ep1)

3D printers often also come with a handbook and some default models that are ready to print which are reading though and trying to print respectively.

Troubleshooting

Common print quality issues with pictures and suggestions on what to check: Print Quality Guide | Simplify3D Software 

Also, printer manufactures often make a knowledge base (like Prusa's here: Prusa Knowledge Base) or a wiki (like bambu's here: Bambu Lab Wiki Homepage | Bambu Lab Wiki) that has specific information about their printers nad answes many FQAs

3D Filesharing Websites

Thangs (3D printing focused and also shows search results for 3D files on other websites):  Trending 3D models free to download | Thangs
Printables, Prusa's filesharing website (3D printing focused): 3D models database | Printables.com 

Makerworld, Bambu's filesharing website (3D printing focused): MakerWorld: Download Free 3D Models
Thingiverse, one of the earliest and largest 3D filesharing sites (3D printing focused): Thingiverse - Digital Designs for Physical Objects

There are many more, but these are some of the largest sites and the ones I have the most experience with. I also recommend following and buying models directly from good designers as they are often high quality, and it supports the community. I personally recommend checking out the themed contests that some sites host (e.g. Printables and Makerworld [Thingiverse used to have a page for them but stopped organizing them a few years ago, you can still find them if you know what the contest's tags were]) as the winners are a great curated selection of models for the contest themes like holidays, useful tools and community projects. As of the time of writing this circa 2025 many existing sites are competing with each other, so things are constantly changing but I would generally recommend first looking for files on Printables or Makerworld if you just want something interesting to print (particularly contests) and using Thangs to search if you are looking for something specific.

Other 3D File Sources

A great way to get 3D files for terrain maps e.g. mountains and watersheds: TouchTerrain: Easily Create 3D-Printable Terrain Models (version 3.6) 

Free online Lithophane maker: Image to Lithophane 

NASA 's small but interesting collection of space related 3D files: Models | 3D Resources 

The NIH's collection of biology related 3D prints (be warned many models are difficult to print with a FDM machine and/or require a lot of post processing): NIH 3D
Sketchfab (not just for 3D printing but they tend to have very good 3D scans of objects in museums): Popular 3D models - Sketchfab  

Cool 3D printing Projects

3D printable headphones: head(amame)

Other

Find a specific Filament Color: FilamentColors 

Find More

Other good places to find more information on 3d printing are:

The 3D printing subreddit: https://www.reddit.com/r/3Dprinting/
The 3D printing forums for your 3d printer's manufacturing
Google
If you are going to ask a question on a public forum, please google it first as someone has likely already had the same problem as you and posted about so it's a faster way to get an answer

Get in touch with me. Simple questions I can add to the website, and I can consult for more complex 3D printing issues