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Cool, so open up the windows search menu and find "Create and Format Hard Disk Partitions". Open it.
Right click on your main partition and shrink it by however much space you want for Ubuntu (generally a minimum of 20 GB). You should be left with unallocated space.
Once you have your drive with Ubuntu, chuck it into a port and hop into your boot menu in your UEFI. Select your USB to boot off, and it should boot into a menu. The settings are up to you, but when you reach the partitioning menu, select "Something else". You'll be presented with a list of partitions, select the free space. Set the size to equal the size of the free space. Use it as Ext4, and ensure your mount point is /home. After that, follow the prompts and finish your personalisation. This includes time zone and accounts. After that it will complete the installation!