normality of variable

There are two main methods of assessing normality: graphically and numerically.

Graphical interpretation has the advantage of allowing good judgement to assess normality in situations when numerical tests might be over or under sensitive, but graphical methods do lack objectivity. If you do not have a great deal of experience interpreting normality graphically, it is probably best to rely on the numerical methods. SPSS Statistics allows you to test all of these procedures within Explore... command.

Reference: https://statistics.laerd.com/spss-tutorials/testing-for-normality-using-spss-statistics.php

Then what to do if the scores is not normally distributed nor a straight line?

It can be checked by using a scatterplot. When you look at a scatterplot of scores, a straight line should be shown (roughly), rather than a curve.

Thanks imir. How about linearity?

It can be checked by inspecting the histograms of scores on each variable. If the scores are normally distributed, you could see a bell-shaped curve.