How to say a big number?

1,200,000

one million (and) two hundred thousand. British English requires the “and” while it’s optional in American English.^[1]
one million two hundred thousand
one point two million
one million (and) two (casual, ambiguous)^[2]

1,000,002
one million (and) two
one o o o o o two (OK, but cumbersome, text mode)

1002
one double o two (text mode)

References

1. Michael Swan; . Practical English Usage. . , (4th edition): 322.9 [].↑
2. Tony Stewart EE75. Read 2,000,005, use oh (o) or and?. . 2022-09-12 [2022-09-13].↑