Dear,
I am just wondering: what would be the difference between "clean" installation and manual partitioning?
Does Zorin OS do good job if I go straight forward without bothering to have swap and other partitions? Do you recommend just to go: ERASE... and install Zorin OS?
Thank you!
I assume that by "clean installation" you mean using the entire drive. The only difference is that you must choose and specify how much and which sections of the drive to use, although even this is neatly presented to you.
The only question is: do you need to use reserve space for other things like additional operating systems, swap or extra storage? If not, then go ahead and use the full drive during installation. You'll always be able to create those partitions at a later point if you need to. The most important consideration is whether or not you want to dual-boot i.e. have multiple operating systems, especially with Windows.
No Windows -- never more 
THANK YOU VERY MUCH!
Yep, no worries. You'll be fine with the full disk installation, and as mentioned you can always change things around later. Make sure to read the help pages for details on how to things like creating the bootable USB, verifying the integrity of the ISO file and so on. Good luck!
EDIT: may want to checkout this walkthrough as well:
Just remember if partitioning manually to an SSD, no swap file/swap area is needed.