How do I properly flash a ROM?

[deltapancake]

Hello guys,

TP2 SPRINT CDMA user here and I have a few questions.

Story: My phone was unlocked for me by a friend and Mr. ROM was flashed. He also gave me a SIM card and saved my contacts on there.

The phone has been glitchy: Screen goes blank, won't turn on for a few minutes, twitter app doesn't work, can't read facebook comments etc...

Situation: I want to learn how to do this once and for all but I am a complete newbert when it comes to Flashing Rom's and transferring contacts (I do not want to lose my phone #'s)

Goal: I would like to flash something that is fast, stable, and reliable.

I only have a slight idea of how the process works, but with a descriptive tutorial I think I should be able to do it, so I'm asking your guy's help.

I don't know how to use a SIM card
I don't know how to properly flash a ROM
I don't want to lose my contacts

PS: I've read those stickied threads on how to flash a ROM but it's kinda confusing and I'm lacking confidence to attempt something like that on my own w/o guidance.

Thank you.