Thanks to all here because you help me to understand and i understand now. Thanks very much :*

Thanks, but i read on internet that keypool is for like when i receive bitcoin from 100 people, and if is set to 100 and i receive 101 transaction, i lost that 1 transaction because is set to 100. Because if i have one single address in my bitcoin core wallet, and  that receive transaction is keypool, because every transaction have a key and any transactions is like key and is set to 100. Thats means i can receive only 97 transaction(send or receive). Is true or not, i want to know ?

But with keypool, what is this keypool for, and what means 100 in bitcoin core ?
And what is if i have in my wallet 2 address and i backup my wallet, and then i import my private key, or i put backup in my wallet, and i lost my funds because i see on internet that is 100 address that they isn`t used and when i put my backup or import key in the wallet, the balance appear 0 because that 98 address is not used, and was used only 2.

I don`t understand, some people say it`s not bad thing to use single address, and some people say it`s not good to use single address.
If i use single address for one transaction, and 2000 people send funds to my address, i lost my funds, because i see that bitcoin core have 100 keypool

 Please i want to know if in my wallet i have one single address and  receive more transaction on my single btc address it is ok ?

I heard that is a bad thing to receive more transaction to single address, but i see on internet that some people want donation from people to single
address like paper wallet. Do you know if i have bitcoin core wallet with full synchronizing, and i have single address like receiving address, it is ok,
because i see that paper wallet have one single address and people that request donation have one single address. I look days to internet and i see a lot of help but i want to know more to be sure.


PS: I don`t want donation, but i ask because if i want to sell something to know if is ok to receive payment to one single address.