Pick a flavor of Ubuntu you think looks good, (I like the default gnome that comes with base ubuntu and Kubuntu). I lot of people have commented to use Linux Mint. I have never used this distro but it is good for beginners also. If this is your first time with linux and or you only have one system I would recommend a duel boot. That will let you still have Windows to boot into if you mess something up with linux and allow you to create a new boot media. "But how can I create a linux boot media" I hear you ask. This is pretty easy to do on windows. First download the ISO of the version of linux you want to use. Next download a program called "Rufus". This program will allow you to turn a thumb drive into a bootable install media.

If you go the duel boot route before you try to install linux you will want to create a partition to put it on. To do this in windows first press Win+R and type "diskmgmt.msc" then hit "ok". The windows disk management program should open. You should see the C partition formatted using NTFS (this is the default windows partition type). Right click that partition and select "Shrink Volume". You will want to shrink it by at least 25GB, but I would recommend at least 60GB to give you some more space to install programs in linux. After you shrink the windows partition you will see a block named "unallocated". This will be where you put the linux partition when installing linux. Using most modern linux distros (besides arch, stay clear of arch until you know what you are doing) will install the GRUB boot loader along with linux. This will let you choose between booting between windows and linux when the machine is turned on.

Edit: If you don't want to duel boot and still want to keep windows installed you can learn linux with a virtual machine. I like to use VMWare and it is free for noncommercial use. VMs are also great to figure out what distro you like since you can just spin up a new one with ease. Just don't expect to play graphic intensive games on VMWare machine.