1. Everyone starts out with no experience.
2. See above.
3. Buy parts, get a screwdriver. Put everything together. It's like building with legos thats how easy it is.
It's easy, there's just a few things that could confuse you, like putting thermal paste on the CPU, and installing the PSU wires.
There's some good guides out there, especially by Linus from NCIX tech tips. Look up NCIX on YouTube.