Do I need to re-format the whole drive to use a partition with APFS or I can just format one partition?

Pretty much the title, I was reading a guide for my X220 to install high sierra and I might be confused but this is what it says:

From the macOS Utilities screen, launch Disk Utility

In Disk Utility, click the View menu and select Show All Devices Select your target disk (select the physical disk, not a volume on the disk) and click Erase If the target disk is already in APFS format, or if multiple partitions exist, it may be necessary to click Partition and remove these partitions Some users have reported installation issues when more than one disk is installed (primary bay + mSATA). It may be necessary to temporarily remove any additional disks. You must end up with a single partition on the disk as described in the next step 

Name the target disk Macintosh HD, select Macintosh OS Extended (Journaled) format and GUID Partition Map scheme, then click Erase Do not select APFS format as this will prevent the installation from completing. The file system will automatically convert to APFS during the installation process if your target disk is a solid-state drive (SSD).

I already have an HFS partition, can I just install it on that and have the installer convert this to APFS or it will fuck up the rest of my disk as well?

Thanks