Best to check your university's style guide for this, if one is accessible.
A bit of advice I had when I asked my supervisor a while back, he said that it is important to keep it concise and to the point - maximum of one page, but ideally, less than this. It should include:
acknowledging key people - usually advisors/supervisors, family and other academics who have had a significant contribution to your understanding of a topic. Also, if anyone specifically provided practical assistance related to your dissertation.
acknowledge groups, this would include forums, sites like Stack Exchange etc.
Only those who have had a significant impact on you completing your work. The order is up to you - however, one way to proceed is to put the most significant first. Then a final sentence/paragraph for your family (if you wish).
What you shouldn't do is to list every single person who did something. For one thing, it'll make this section too long.
For each, write a sentence of their contribution. I found that the people assessing my dissertations (Honours, Masters and PhD) did not even acknowledge the page as it is often considered to be a personal page.
Just to repeat, this was the advice I was given when I asked about this - there is no universal template for how this section is written - but, consult your institution's style guide to see if they have any guidelines, also, ask to see other dissertations and perhaps go by what you see in them.