Before you do anything else, make sure you can build the template. You need a recent version of LaTeX, MacTeX for Mac or MikTeX for Windows.
When you have everything installed, try building dissertation.tex preferably using LatexMK. Make sure that the bibliography is being parsed correctly. If you are using TeXStudio or a similar program, you might want to change your default compiler to LaTeXMk.
Once you have managed to build dissertation.tex, consider reading through SSEthesisPreamble.sty and SSEthesisLayout.sty as well as the .tex files in the chapters folder to get a sense of what is going on under the hood.
According to SSE guidelines, text should be in the font Garamond and headlines in Century Gothic. Century Gothic is not easily available in LaTeX (if one does not use XeLaTeX and system fonts) but the similar Avant Garde is, using the Avant package. Instead of Garamond, we use the ebgaramond-maths package to get the similar EB Garamond.