Many stats packages allow you to view the adjusted means/marginal means/predicted values of a model (e.g., R's lsmeans, Stata's 'margins', SPSS's 'Estimated Marginal Means'; for more info., see https://www3.nd.edu/~rwilliam/stats/Margins01.pdf).
Marginal means are often presented with a t/z value, a p value, and confidence intervals.
1) Are these one-sample tests?
2) What is their importance? If, for instance, I have a marginal mean which does not reach the threshold of significance, can I still use it to describe my data? What does it mean if it is not significant? (ignore the dubiousness of null hypothesis significance testing for the sake of the question, since they still dominate many journals in the psychological sciences).