There are three options how to buy bitcoins or fund your wallet.
Buy Bitcoins with fiat
Click "Buy" button on Bitcoin page.
Select your country of residence, click "Buy" button on preferred provider and follow the instructions.
Crypto deposit
Fund your wallet directly with bitcoin transaction: go to Receive tab, copy your wallet address and make crypto transaction to it from external service or exchange.
For this type of funding there is no maximum limit on the amount of the deposit.
Exchange
Exchange from another crypto to bitcoins: go to Exchange tab and follow the instructions.