When learning Japanese it’s often recommended to start learning Hiragana and Katakana to start out. Kanji comes later but these are the basics to getting you started with reading and writing. Romaji is simply romanization (or English writing) of Japanese characters. Personally, I wouldn’t become dependant on romaji, you will see it used at times in Japan and it is helpful to know but if your goal is to learn Japanese you’ll want to avoid becoming dependant on it.
Below I’ll post the Hiragana and Katana character charts but you can easily find them just about anywhere online and in books.
Remember that the “R” row doesn’t sound like the English “R” nor does it sound exactly like the English “L” which some will suggest it does. It sounds more like a combination of both letters. A tip was given to me by a native Japanese speaker: Make both the “R” and “L” sounds and pay close attention to how your tongue sits in your mouth when you make the sounds then try positioning your tongue in between those spaces to make a combination sound. It’s tricky since it’s not a natural movement for many but with enough practice, you will get it in no time.
In terms of Kanji, we are talking thousands of characters. Don’t be discouraged though most places like schools, books, the JLPT have recommended Kanji to learn. There may be a lot but if you dedicate enough time and patience, learning them won’t seem so hard. Everyone has a different opinion on how to learn Kanji but mainly I suggest whatever works best for you personally.
So there you have it a simple introduction to the beginnings of the Japanese language.