The Ubuntu installer starts. First, select your language:

Choose your country:

Let the installer detect your keyboard layout (you will be asked to press a few keys, and based on the keys the installer will detect your keyboard layout):

If you want to install a desktop system, you can leave the default hostname unchanged:

Now we must select a mirror from which the installer will download the needed Ubuntu packages. Select a mirror that is close to you:

Afterwards, a few packages are being downloaded:

Now we must partition our hard drive. If you have at least 5GB of free, unused space (i.e., not used by your Windows partition), you can select Guided - use the largest continuous free space, otherwise you must downsize your Windows partition. This can be done by the Ubuntu installer, so select the Guided - resize ... option:

Before the Windows partition can be downsized, we must allow the installer to write the prvious changes to the disk:

Next, specify the new size of your Windows partition:

Afterwards, the Windows partition is being downsized:

The installer will now automatically create a / and a swap partition for Ubuntu on the free space. Answer the question Write changes to disks? with Yes:

The free space is now being partitioned: