If the importance of a logo design is not clear to you then it can be summarized in a way that, a logo is unique in its appeal and it is the cryptogram of the organization. Therefore, the logo design represents the individuality, nature, and uniqueness of that organization graphically.
Royalty free vector is a good way to earn some money. You can create a logo, which you can sell to any organization. However, the selling process is not direct. For this, you need to upload your vectors to any online stock agency. They will buy your brainchild and will pay you in return. The amount of money depends upon the website itself. The mode of payment varies too. Some websites offer download options which are subscription based. Their pay packets are relatively small. While some royalty free vector stock agencies provide ‘pay per download’ mode where you will be paid each time when your vector will be downloaded. There are some websites offering even both the options.