Here is a discussion on this Stack Exchange Discussion and then here is a working example Poster Template referenced in the previous discussion. It is the one I would reference to my students.
Note: You do not have to have an account with
latextemplates to download the *.tex file and all supporting files.
I would suggest that you download all the files including the pdf to your computer. Then rename the pdf so that on subsequent compiles it will not be overwritten.
Then, without changing the downloaded example in any way, compile it and verify that you get the exact same pdf output.
Finally copy all of these file to an archive directory, so that if you make a change which causes serious problems, then you still have the original files to compare to.
Last, a bit of advice on using BeamerPoster. Because it is creating a large single slide, it is very easy to make an error and not be able to get it to compile. So, only make changes in a single area for the poster and then recompile.
Also, I strongly recommend that you read the manuals for beamerposter, beamer, and tikz, because there many available options. p.s. Use www.texdoc.org to quickly obtain the manuals.