How do i know when i need to use sss or sas in geometry? i'm having a lot of trouble understanding the difference and when to use each one. in advance : d

SSS = Side-Side-Side
If three sides of one triangle are congruent to three sides of another triangle then the triangles are congruent.

SAS  = Side-Angle-Side
If two sides and the included angle are equal to the corresponding parts of another triangle then the triangles are congruent.'
The angle must be formed by the two pairs of congruent, corresponding sides of the triangles. If the angles are not formed by the two sides that are congruent and corresponding to the other triangle's parts then you cannot use the SAS postulate.

you will notice that the main difference between the two postulates is that the SAS consists of an angle and the SSS does not.

hope this helps :)