Hello,
1) Price filter generated automatically depending on price of products that you have.
2) This is Newsletter promo popup (Theme Options > Header builder > Newsletter > popup content). This popup is created using Static Block, so you can edit Static Block content from Static Blocks > edit newsletter block. Don’t forget to enable page builder for the Static blocks https://xstore.helpscoutdocs.com/article/47-static-blocks
WooCommerce coupons you can create from WooCommerce > Coupons
3) What description do you want to add? Provide an example for better understanding.
Regards