woocommerce display products from two categories combined

If you’re using the products shortcode, add operator="AND" to the shortcode args.

Thanks for your help, but maybeI’m not writing it correctly.
I’m sorry if I seem dense..but like this?

[products categories="contemporary AND lighting"]

because that doesn’t work.
I’m getting a lot of stuff that doesn’t belong to either category

That shortcode accepts ID or SKUs for products: https://docs.woocommerce.com/document/woocommerce-shortcodes/#section-10

You need this one: https://docs.woocommerce.com/document/woocommerce-shortcodes/#section-14

[product_category category="contemporary,lighting" operator="AND"]

WordPress does have some trouble with this query if categories have hierarchy though it seems.

I am trying to make an url that would show multiple product categories inside woocommerce shop. I wanted to show just all small vegetable and fruit together.

I have following hierarchy:

Fruit
Small-fru
Medium-fru
Big-fru

Vegetable
Small-veg
Medium-veg
Big-veg
And I tried these urls:

https://my-url.com/product-category/fruit/Small-fru+Vegetable/Small-veg/
https://my-url.com/product-category/Small-fru+Small-veg/

But it did not worked. Is there some solution for this?

Not that way. You can make a new category for the things you want to show. Products can belong to multiple categories. Or you could do it by assigning a tag to the items you want to group:
https://my-url.com/product-tag/sm-veg-and-fruit/