How do you pronounce the Japanese "r"? Is it more like an "l" or something inbetween? Would there be any picture or video explaining it correctly, please link it!
The sound that's transcribed in Romaji as 'r' is what's refered to in phonetics as an alveolar flap (or alveolar tap). It's a sound made by quickly tapping the tip of your tongue on the alveolar ridge (the same place you use to pronounce sounds like 't' or 'l') and to native American English ears sounds somewhere between an 'r' and an 'l'.
If you are an American English native speaker, you probably already make this sound when speaking your own language. It's what's the double-t is pronounced as in "better", for example.
I pronounce it as a singular Spanish 'r'. If you can pronounce Spanish, this will help you. If not, it probably won't. Although I've often described it as close to a 't' or 'd' sounds (as @oren Ronen mentioned with 'better').
It's in between the English "l" and "r" sounds. Make a "l" sound, but sweep the tip of your tongue back without letting it touch your hard palate.
Tofugu video I've used.
This is the best video I’ve found about pronouncing the Japanese r. It describes it as the sound between d and l, and has lots of diagrams about where your tongue should be when you say these different sounds.
I found a video which shows a shadow of the tongue position when a native speaker uses ra etc. There is also some assistance using a Canadian English dialect which may add value.