I noticed there is no buy button in my theme block, is there any code I can add to add a buy button? Thanks.
Too broad of a question so you only get broad answers.
That is an advanced theme customization that will vary wildly among themes.
See the themes product template sections and snippets for how it uses it’s own buy-button block.
You will need to learn theme architecture
https://shopify.dev/themes/architecture/sections
If you need this customization built then contact me by email for services.
Contact info in forum signature.
ALWAYS please provide context, examples: store url, theme name, post url(s) , or any further detail in ALL correspondence.