An address is checksummed if it uses both upper- AND lowercase letters instead of just lowercase letters. Checksummed addresses are meant to help prevent users from sending transactions to the wrong address.
How to checksum an address:
The easiest option is to get a checksummed version of an Ethereum address is to open the address on etherscan.io and copy it from there.
e.g. https://etherscan.io/address/0x448E4E6DD37523A5c7804D75a67754c24bFbFb32/
