I have some problems finding how to add quantity to my product
is this future available in wave
It's this box here, on the invoice creation page.
You'll be able to mark the quantities of product there. Do you see the same thing? Let me know if your Invoices page is having issues loading.
I meant the quantity of my stock
like how many i have from this product
I apologize for misunderstanding your question. Wave doesn't currently have an inventory management feature.
Most Wavers operate businesses that offer a service, rather than products. Our focus is always on building features that can help as many Wave users as possible, so tools for inventory management or for making purchase orders, for example, aren't our priority at this time. If you'd like to learn a bit more about how we choose was to build next for Wave, I recommend checking out this post.
With that said, we do have a bit of a workaround to allow you to keep track of the value of your stock, even if you can't keep track of the number of items. You can find that over here. I know it isn't necessarily perfect, but it works for some other Wavers, and it might help you as well.