Since your question seems a little vague to me, I'm gonna cover a few different things about numbers. I assume you're talking about spoken form, and not the written form, but I'm gonna mention that anyways.
With spoken form, you will learn that, and it's actually simpler to some extent. You pretty much need to learn the numbers 1-10 in order to get all the way up to 99. This is because the way that you say numbers in Japanese essentially "spell out" the number. For example, the number 11 is literally spoken as "ten one", and 20 is said as "two ten". As can be concluded, 21 is said as "two ten one", and so on.
This applies basically until you get into the hundreds and thousands. With the word for hundred being pronounced "hyaku", you can imagine it may clash with a sound coming before it. So, the Japanese language has conveniently made it so that the pronunciation of the word changes slightly. For example, the word 300 would be pronounced as "san hyaku", but because it's tough to say that fast, you slur the "h" a bit, and end up with "san byaku". The rules for skewing the pronunciation are rigid, though, so watch out. Unfortunately, you can't just pronounce everything how you want to. ;)
One more thing about the larger numbers is that, traditionally, Japanese would group numbers into sets of 4 digits. Unlike in the majority of other languages, which group digits in sets of 3. For example, a million is probably written by you as 1,000,000, with the digits being separated into threes. However, for japanese, they would be separated like this: 100,0000, into groups of 4. (Don't worry if u don't see this consistently, though, because evidently, western culture has had an influence on Japanese culture, but this demonstration is simply to illustrate the point that I'm about to make).
This is just to show more clearly that once you get to the number 1,0000, or more familiarly written 10,000, (pronounced "man"), you need to say "ichi man", when talking about only one unit of 10,000. This contrasts to how you don't use "ichi" before 1,000, 100, 10, or any smaller numbers when talking about a singular set of that number. It's interesting but you will pick up on these exceptions in speech.
Finally, in written form, the traditional characters for digits are very different from the ones you're probably used to (called Arabic numerals). People don't really use those, especially for large numbers, because it's a lot more tedious and large numbers end up taking way more space than Arabic numerals. You may see some of these characters in words that use counters and generally small values, but most of the time, I've seen people use Arabic numerals.
Anyways, I hope this helped, and I wish you luck! 😊
