I'm confused about the difference between the significance level for hypothesis tseting and the level of confidence when estimating. Could someone please explain it to me?

Also, i'm stuck at this question:

If the null hypothess is not rejected at the 5% significance level,

a) Does this necessarily imply that the estimated mean is contained in the 95% confidence interval for actual population mean?

b) Does this necesssarily imply that the estimated mean is contained in the 90% confidence interval for the actual population mean, if the observed sample mean is bigger than the population mean?

thanks