To make the template your own, you need to know the fundamentals of HTML and CSS. It is important to understand the differences between the two languages, the syntax of each language, and some common terminology to effectively use the template.
There are numerous resources on the internet that will assist you if you need help with HTML, CSS, Javascript, etc. 100% of your questions can be found via a Google search as someone has already asked the same question prior to you.
Nevertheless, there are some specific online sources that will provide plenty of assistance. Here is a small list: