Lizzy here, I’m a Shopify support Guru.
Yes, you can absolutely post your own products on a Shopify store! We have many merchants using the platform that make or manufacture products themselves and then sell with a Shopify store.
What sort of products do you have for your online business? Is it something that you've already been selling, or will this be a new business for you?
If you're working with a supplier who will be shipping the products for you as well, you may find it useful to set up custom fulfillment options in your admin. With custom fulfillment, you can adjust your settings so that your supplier is emailed every time an order for the product comes in! This help doc explains how to set the feature up.
Please let me know if you have any further questions about this that I can answer!