Kanji was introduced to Japan nearly 2,000 years ago. It is said that 50,000 kanji characters exist, though only about 5,000 to 10,000 are commonly used. After W.W.II, the Japanese government designated 1,945 basic characters as "Joyo Kanji (commonly used kanji)," which is used in textbooks and official writings. In Japan, one learns about the 1006 basic characters from "Joyo Kanji," in elementary school. A lot of time is spent at school learning kanji.
It would be very helpful for you to learn all the Joyo Kanji, but the basic 1,000 characters are sufficient to read about 90% of the kanji used in a newspaper (about 60% with 500 characters). Since children's books use less kanji, they would be a good resource to practice your reading.
If you want to learn Japanese writing, start with hiragana and katakana, then kanji. Hiragana and katakana are simpler than kanji, and have only 46 characters each. It is possible to write an entire Japanese sentence in hiragana. Japanese children start to read and write in hiragana before making an attempt to learn some of the two thousand kanji commonly used.
Here are some lessons about Japanese writing.