While practicing your reading on website might be interesting from time to time, I'd suggest sticking to your books/alternative sources until you have at least learned both hiragana and katakana. Kanji are complex, so mastering the basics first and ignoring the kanji for the time being is probably a good idea.

If you have sources to practice reading without having to read Kanjis, I think you can ignore them for now, until you get a bit more comfortable with the basics. However, you WILL have to learn them eventually if you want to read most stuff on the internet/books. If you ever get trouble remembering kanjis, I have two solutions I used in my studies that might help you too. 1- Reviewing the Kanji : This website is meant to help you remember Kanjis learned through Heisig's ''Remembering the Kanji'', a textbook. If you are not interested in buying/finding it, skip to option 2. This website allows people to share mnemonics for over 2000 Kanjis and features a Spaced review flashcard system. (Each time you remember it right, the next time it appears get further away, and resets when you fail it) 2- Anki: This software is completely free on PC and is very customisable. It is a spaced flashcard program that allows you to build you own cards, may it be for science, grammar or even words and Kanjis! In my opinion it works better as a way to review vocabulary, but I guess you could use it for Kanjis too. I hope it helps!

Yes, you will have to learn it. Japanese has a lot of homophonetics (words with different meanings which sound exactly the same). 合う (to fit) and 会う (to meet), both あう 買う (to buy) and　飼う (to keep), both かう　 But when I see your question like "But I do not understand how to read something when kenji,katakana, and hiragana are all used at the same time side by side." I would recommend to start by zero and grammar first anyways.

I'm using the "easy way to learn hiragana" system on Misa's website japaneseammo.com. She suggests buying Japanese children's books to practice reading because they don't have kanji - or at least have minimal kanji. Hopes that helps!

The Furiganizer is a pretty useful tool if you want to read passages of text which contain characters you don't yet know. Just paste in any Japanese text for readings and definitions. No furigana for katakana words though, you just have to learn it. http://www.furiganizer.com/