First you need a 'host', Zymic for example is a free host and i admit, it has great features. So since you are registered you can now have free hosting here from your ZCP (Zymic Control panel) from the main website... so create an account.. or you probably already got one ?
Or you can have a paid host... check on Google... their are millions of hosts

(no probably less)
Anyways once done, you need to access your 'host' and put the template files INSIDE the host... to do that you connect to your host via FTP (on Zymic) or other sites.. and providers offer File managers to upload files to the host... but they ALWAYS give you FTP (its faster and easier)
So you will have an FTP adress, a username, a password and a port (usually 21 i believe)
You will need an FTP client (a program on your PC that will connect you to your host).. again check google for that.. their are planty of free FTP clients... my personal favorite Smart FTP (free).
Once installed, usually on TOP of the program you can put the FTP address, the Username and the Password (you get that info from the ZCP...)
Once connected you simply see what ever is on your host... its just a folder with template files, the FIRST page of your template will be called INDEX (extension may vary such as .html .htm .php.
So what to do ?Well to start of Download a template from Zymic (again free) and Upload the template to your site via the FTP, make sure that you upload the files and not the folder of the template... see you have a MAIN root of your host, if the index.html file is in a folder called /somestuff it will ONYL show if you are at : mysite.com/somestuff ... so make sure the index.html the images folder and the style.css (usually the 3 stuff that are in a template) are in the correct root (the very first folder of your site !
once uploaded go to your site and see for your self...
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To modify your template, well open up the page .html or .php or .css with WordPad or Notepad... or any text editor (no need of a Fancy program) and modify what is inside.
i will go with the above and say you need to know a little HTML and CSS to do that.Took me 3 month to understand CSS fully, i think i can pretty much do what ever i want with CSS, and over a 6month to understand HTML fully. Add that a full year of practice and you can do pretty much what ever you want...
And the final touch.. to get it faster... you need to be a part of a great community such as Zymic... so you can get all the help you need !