Re: What will happen in this install ...?
The installer should give an option to install in the free space on the drive. Make sure you have enough free and unpartitioned space to use. The installer can resize existing partitions to make space, but if you do that make sure to back-up your files, as resizing partitions can go wrong. Just avoid the options to replace or upgrade existing OSes, or the option to use the whole disk!
The installer also has the option of manual partitioning within the installer, which you may prefer. In that case, create a root partition for the system (10–20 GiB, ext4, mounted on /), a swap partition (2xRAM), and a home partition (the rest, ext4, mount on /home).