sudo is a way to elevate your privileges to those of the root user, i.e. the system administrator. touch is a command that changes the last-modified time on an existing file, or creates an empty file with the given name if it did not exist already.
In this case, given that you intend to mount an NTFS volume with Steam games, you should pick a name that matches its purpose, something like… 
sudo touch /etc/systemd/system/steam-ntfs-drive.mount
Okay, here @linux-aarhus is unintentionally making things a little more difficult than he should. 
Your profile says you’re using Plasma, so use kate or kwrite, both of which are GUI editors with polkit support. This means that if you’re trying to edit a file belonging to the root account — as everything under /etc does — then they will prompt you for a password when trying to save the file.
The value to be filled in for What= can be gleaned from looking at…
ls -l /dev/disk/by-uuid/
For instance, on my system, the above command outputs the following…
[nx-74205:/dev/pts/3][/home/aragorn]
[aragorn] > ls -l /dev/disk/by-uuid/
total 0
lrwxrwxrwx 1 root root 10 Jun 28 05:29 1aedac7f-403b-4d85-9643-0d622be75453 -> ../../sdb2
lrwxrwxrwx 1 root root 10 Jun 28 05:29 3f1852bc-be95-4e42-8d46-25bafac4ce79 -> ../../sda3
lrwxrwxrwx 1 root root 10 Jun 28 05:29 6d475769-c92c-4935-b2af-a53d29dcd898 -> ../../sda7
lrwxrwxrwx 1 root root 10 Jun 28 05:29 6e756bf9-2d7c-401a-a0f3-bb4ea3b824a9 -> ../../sda6
lrwxrwxrwx 1 root root 11 Jun 28 05:29 6fbd221f-5d46-40f0-9fbf-4479d73874b4 -> ../../sda10
lrwxrwxrwx 1 root root 10 Jun 28 05:29 8462b14d-4a97-4383-a55d-61fcd136aeb9 -> ../../sda5
lrwxrwxrwx 1 root root 10 Jun 28 05:29 889d4e36-e279-4b82-838a-a5c1d4964e1a -> ../../sdb1
lrwxrwxrwx 1 root root 10 Jun 28 05:29 8de45432-efe5-4d76-beb9-fcb3247a063e -> ../../sda4
lrwxrwxrwx 1 root root 10 Jun 28 05:29 924f11d8-4bec-49a6-852e-033ce5e3d6a3 -> ../../sda2
lrwxrwxrwx 1 root root 11 Jun 28 05:29 bdf6a9f6-a2a7-47a0-ba6f-7bbf71a01a95 -> ../../sda11
lrwxrwxrwx 1 root root 10 Jun 28 05:29 CEF6-EF5C -> ../../sda1
lrwxrwxrwx 1 root root 10 Jun 28 05:29 db2385c9-2715-408e-96b4-52086a0292fe -> ../../sda9
lrwxrwxrwx 1 root root 10 Jun 28 05:29 e3fe76c9-8dea-4a27-8f47-839bb464f022 -> ../../sda8
If you read my tutorial above about UNIX permissions and file ownership, then you will see that those are all symbolic links. So you need to fill in the full path to the symbolic link that corresponds to the partition you will be mounting. For instance. …
What=/dev/disk/by-uuid/6fbd221f-5d46-40f0-9fbf-4479d73874b4
The Where= entry should point to the directory (“folder”) where you want this filesystem mounted. This directory must exist and should for good measure be empty, because — as you can read in my second tutorial above about working with additional “drives” — once something gets mounted to a directory, whatever was in the directory before will be obscured until the filesystem mounted there is unmounted again. For instance…
Where=/home/your-user-name-here/Steam
However, given that it’s an NTFS drive, you will also need to uncomment the #Type= and #Options= entries — i.e. remove the “#” in front of them — and fill in the proper information. Something along the lines of…
Type=ntfs-3g
Options=auto,nofail,uid=1000,gid=1000,utf8,umask=022,defaults
Note: There must be no spaces in between the mount options.
Lastly, for the Description= entry at the top of the file you’ll want something like…
Description="Steam Games on NTFS Volume"
But please, please, please, if you’re absolutely new to GNU/Linux, then do read my two tutorials as I posted above. You’ll thank yourself later for doing so.