To learn kana you need to write them out over and over and over until your hand hurts. That's 48×2=96 characters, so this is a very doable task. Consider it a test for how serious you are about Japanese. After that, consider using
Anki - friendly, intelligent flashcards and a decent textbook to take example sentences and vocabulary out of.
If it must be entirely computer-based and you want to be spoon-fed, Yamasa's
online thingy might help you. I've used it myself on occasion since they give free access to it to full-time students. It follows みんなの日本語 up to lesson 50. The first few lessons are free. They have listening, reading, and sentence writing practice, and someone corrects your written work for you.