Japan's language and culture are quite different from those found in the West; in fact, the Japanese language is part of its own family, unrelated to most other languages in the world. This is part of what makes learning Japanese so challenging for English-speakers compared to languages like French or German, which are more closely related to English.
The first thing that a completely new student of Japanese should know is that they'll be learning to read a whole new type of script. Actually, three different types of script are used to write Japanese: kanji, hiragana, and katakana. Katakana and hiragana, which together are called kana, are both phonetic alphabets, meaning that the characters represent specific sounds, just like the letters of our alphabet do. Hiragana uses round shapes to represent traditional Japanese words and function words. Katakana is used for words that are taken from other languages or ones that sound the same as foreign words. The third type of script, kanji, consists of Chinese characters that were adopted into Japanese. These characters are used for nouns and the roots of the verbs and adjectives.
Japanese uses horizontal as well as vertical writing. Vertical writing is the traditional way of writing that is used by the government, schools, and journals and in literature. In vertical writing, the text is read from top to bottom and right to left. Books written in this style are opened with the spine on the right; the "last" page is actually the first page. Horizontal writing is also used in modern times, especially for publications related to math, science, or computer programming, where equations and/or code may need to be included. Horizontal texts are written from left to right, and these books open with the spine on the left.
Japanese grammar is also quite different from that of English. In English, sentences are typically written in the order subject-verb-object, but in Japanese, sentences are usually structured as subject-object-verb. However, Japanese grammar is also simpler in some ways. For instance, Japanese nouns have no plural forms, and there are only two verb tenses: past and present.
Once the structure of the language is established, the only thing left is to learn the vocabulary. For this, there are plenty of online resources that can be useful, including word lists, videos, flash cards, puzzles, and games. For more complex words, a simple peek at the dictionary is often enough to learn any word of interest. Reading books in Japanese can also help English-speaking learners to pick up new words, provided that they have a glossary. Usually, people learning Japanese start out with learning the katakana and the hiragana; because they are phonetic, it is easier to start with these alphabets. Knowing these writing systems can help you as you come across unfamiliar words. It's also useful to incorporate audio resources into your learning, as mastering Japanese pronunciation can be tricky without examples to learn from.