How do I use this library to execute smart contract functions?

[dimitarvp]

I am fairly new with ETH and smart contracts but found myself in a position where I have to mint an NFT -- which is basically calling a function of a smart contract (which is already on the ETH network).

My blocker with ethereumex and exw3 is that I still can't quite figure out how to sign a transaction and then send it (through eth_sendRawTransaction) -- I am able to construct an unsigned transaction otherwise.

During my search I figured I'll also try this library but sadly I can find no example how to do this exactly.

I am aware my question is a newbie one and I'll be grateful for any pointers that can help me solve this. (One possible hint is that calling a smart contract function is in fact a signed ETH transaction, is that true?)