Details of relevant skills and experience. But do not go too detailed. There should be enough information to convey your competence without being overwhelming. The person reviewing your resume doesn’t have time to read a novel — make sure it is succinct. Put the most relevant skills/experience front and centre and be ready to back them up. Nothing hurts your chances more than failing at something you’ve listed in your resume.
> where can I get good latex templates for applications?
Don’t bother — just use MS Word/Google Docs/Apple Pages/LibreOffice Writer. They all have templates for writing resume. Just be sure to convert the end result into a PDF.
> which topics should I look at again before a trial working day?
The basics of whatever you are supposed to be working on, I suppose. You can always Google if you don’t know something — so don’t bother rote learning command line opts. Make sure that you are familiar with the environment you are going to work on — things like basic commands, scripting, automation, and other tools. For example, if you are going to be working on remote Linux servers, you need to be familiar with vi/vim. Similarly a Windows admin needs to be competent enough with PowerShell.