A Paired-Samples t-Test compares the means between two related groups, such as comparing the difference between pre-intervention and post-intervention test results.
It is considered a parametric test and is only suitable for parametric data. To check if your data is parametric, please check out the dedicated guide: Parametric or Not Guide (PDF)
If your data is non-parametric you should consider using a Wilcoxon Test.
Click Analyze > Compare Means > Paired-Samples T Test
Within the Paired Samples t-Test box, select the two variables you wish to analyse and move to them to the Paired Variables Box using the right arrow
SPSS will generate three tables, for this test we need two, the Paired Samples Statistics and the Paired Samples Test.
This table shows a selection of descriptive statistics: the sample size of each group (N), the mean of each group (Mean), and the standard deviation of each group (Std. Deviation), best practice is to report them all.
This table shows the specific test results including the t-statistic (t), the degrees of freedom (df) the two-tailed significance or p-value (Two-Sided p), and the 95% Confidence Interval (95% Confidence Interval of the Difference).