Q: How to view mp4 files/touch 4g

How do I view .mp4 files on my Ipod touch 4g?  I copied a .mp4 file to the touch using "FileApp" but don't know how to view the file.

I googled and searched the forums for an answer, and learned every .mp4 file is different and it depends on the codec.

I'm not downloading youtube videos to the touch 4g directly - I'm just copying/pasting .mp4 files I have on my hard drive.  (Many from Youtube)

I'm ready to use a converter program on my Windows PC, but I don't know which program is the best.

I need recommendations from users.

I'm viewing video podcasts from "Videos" on my touch, and it works normally.  But it doesn't show the .mp4 file I copied over.

What do I need to do? 

My questions:

1. Is it easier to view .FLV files on my Touch 4g?

2. Which app lets me view .FLV and .MP4 files? (free)

3. How do I copy them to my touch 4g?
4. How do I convert them to my touch 4g?  (Itunes or separate program?

Thanks a lot.