pre-sale question2 (how to create pack of products)

Hi,

Well, it depends what you mean by "product A if purchased,then give to user product B automatically".
The way the bundle system works is that if you purchase the product A and that B is a bundled product in product A, then the stock of both product A and product B will be updated upon purchase. And you can se the price you want in product A so that it gets cheaper then if you were purchasing the other products of the bundle separately.
If what you mean by "product A if purchased,then give to user product B automatically" is that when product A is added to the cart, all the bundled products in it are added to the cart instead, there is indeed no system for that.

Now, if you just want that there is a special discount that kicks in in the cart when three specific products are in it, I think it's possible to do it with AWOCoupon : awodev.com/products/joomla/awocoupon
I would recommend to confirm with them first as I don't know all the specifics of how AWOCoupon works with HikaShop.