There is some kind of input how bitcoin is start (offer). Is bitcoin is depends on how much we 'invest' so we get different 'amount' in return?
I have a feeling you're asking about the flurry of Initial Coin Offerings (ICOs) that have been taking place. Stay FAR far far far far away from these. Ethereum (ETH)(not bitcoin) has a contract function and these ridiculous "startup" coins are taking advantage of that function to issue "tokens" for their project. Some of these projects are as ridiculous as storing medical records in a blockchain. These ICOs are very lucrative for the developers and a waste of time money and energy for everyone else. They are billed as investments though you get no ownership or control over the operation and some even "guarantee" interest payments. These all are likely to fail in the next few to several months as the interest wanes and fools stop showing up to hand over money.
There are a number of outlets that will sell you bitcoin if you feel inclined to own some. Stay away from all the garbage "investment" schemes that use bitcoin or other crypto.