Thanks for reaching out about this, I understand that navigating the Shopify platform can take a bit of time in getting used to! So I totally understand your concern, and I'd be happy to help and guide you.
I've taken a look at your website and can see that some of the products on your store already have a couple of different clothing sizes, when the dropdown button is clicked on the product page:
Are these the variants that you're having issues seeing on your end? Or have you added other sizes too, that still aren't showing up on your product page?
If you're having issues with seeing new variants on your storefront, I have a couple of suggestions that you can check for on your Shopify admin:
Save any changes you make within the Shopify admin: When adding new variants to your products, remember to save your page before you navigate out of it. This is to make sure that the system will successfully save through your changes to then push the new information through to your storefront. After saving your Shopify admin, remember that it may also take a bit of time for any changes that have been saved to reflect on your storefront. You might need to wait a few minutes, and to also try refreshing your page.
Check for third-party apps: If you're using a third-party app to configure your store's products or variants, it's good practice to double check if the app will override any information that you input within your Shopify admin's product pages. Some apps have the ability to do so, and if they do, you'll need to instead make any changes to your products or variants within the app itself, rather than from your Shopify admin.
If after checking the above you're still unable to successfully add extra variants onto your product page, you can get in touch with our internal Support Team so that we can take a closer look into this issue. At this stage, we aren't able to provide account-specific support via the Shopify Community Forums. So please visit our Help Centre, and login to your store here to reach out to our Support Team. We'd be happy to take a closer look at your account to further help you!
Once you're able to resolve this issue and have successfully added your variants onto your product pages, something that can be worth looking into is adding a size chart to your product pages. Since you're selling clothing, adding a size chart will help customers find and select the correct size before they purchase from you. It will improve your store's overall customer experience, while also potentially minimising any returns or refunds for orders that were made due to the wrong size in being chosen. If you're using one of our free Shopify themes, take a look at our guide here on how you can add a size chart to your product pages. Alternatively, we also have a great range of third-party apps here too, that you can install onto your store to implement a size chart.
Let me know how you go with the information I've laid out above! I'd be happy to help if you have any other questions.