1. Explain it simply
任何 (rènhé) means 'any' in a sweeping sense - any one at all, covering every case.
Word order: 任何 + noun + 都 / 也 + predicate, as in 任何人都能参加.
The 都 or 也 is required; it points back to 任何 to make the statement all-inclusive.
In a negative sentence, 都 or 也 before 不 / 没有 gives 'not any ... at all'.
2. Show examples
任何人都能参加这个比赛。
Rènhé rén dōu néng cānjiā zhège bǐsài.
Anyone can take part in this competition.
都 follows the noun 人
任何问题都可以问老师。
Rènhé wèntí dōu kěyǐ wèn lǎoshī.
Any question can be asked of the teacher.
任何 sweeps over every question
任何人也不能进去。
Rènhé rén yě bù néng jìnqù.
No one at all may go in.
也 + 不 makes a total negative
3. Share a tip
Never drop the 都 or 也 - say 任何人都能来, not 任何人能来.