How do we use Purchase order form?

This is the form number

https://form.jotform.co/202127958826867

I don't want to use stripe here because it is attached with a business account. Can I just send them an invoice?

If you do not want them to charge while they purchase the products then you may add the Purchase Order field switching the Stripe account:

https://www.jotform.com/help/460-How-to-Create-Payment-Form-with-Purchase-Order

Yes, you can configure an invoice. Feel free to check this guide:

https://www.jotform.com/blog/how-to-create-an-invoice

Thanks.