I think I buy windowblinds but...

Yes it does included. Please refer to the list on this link https://www.stardock.com/products/windowblinds/download

and on how much PC's can I use it at the same time? (I have two)

Please refer to this : https://forums.stardock.com/486311/accounts-and-activation-support-faq#pcinstalls

Now i buyd it but skin studio 10 download does not work and there is no key 

and by "Download Software" comes 404 not found 

https://store.stardock.com/Controls/This%20product%20is%20not%20yet%20available

EDIT only the link on the purchase site was broken but on my order history it worket

Product key not require for SkinStudio10.

You can also buy Object Desktop on Sale now which includes WindowBlinds

and many other Great Products

OD is a 1 year renewal

Check it out here : https://www.stardock.com/products/odnt/