...i wanna get into flash animation but i do not know why type of program I should use.
“Flash Animation” is called flash animation because it is animated in Adobe Flash.
...how are the drawings put on the computer? are they uploaded or are they drawn on the computer?
You could scan in hand drawings, but you’d then need to erase the backgrounds of each drawing. That's easy enough though, so if you want to use hand drawings you can. Drawing directly on your computer is the easier and more efficient option though.
...what device would you use?
"Graphics tablet".
Do you record one person reading their lines then take that recording and ive them to the other person o listen/react to while recording their lines?
You could do that. Or you could get both actors together so they can interact. So long as you get good results, you can do whatever you want.
If you really want “Flash Animation” you’re going to need Flash. Having never used Flash, I can’t really offer any specific advice. YouTube tutorials are going to be your friend here.
I’ve recently begun trying my hand at 2D animation. I have a Wacom Intuos tablet to draw on. I draw in GIMP. If I had Photoshop, I’d use that, but I don’t, and GIMP is the open source alternative to Photoshop. I draw my characters in several pieces. Each piece is on its own layer. I then animate in After Effects, as I already own this. Blender is a free open source software platform, that can do everything that After Effects can do.
Again, search YouTube for tutorials. Search for “animating in After Effects/Blender” and “drawing animation characters in Photoshop/GIMP”. You should find what you need. To make your characters talk (and blink, as they require similar processes), you’ll need to search for something like “lipsyncing animation in After Effects/Blender”.
Good Luck!