Please help me understand

[parisse]

If you want to run CAS commands, it might be a better idea to make a CAS program than a Home program, because you won't have to EXPORT a x variable that is a non-CAS variable, may have a value and could interfer with CAS evaluation (especially for a command like solve that auto-quote parts of it's arguments). From CAS enter
dmy():=
BEGIN
LOCAL ab;
ab:=solve(x^2-3=1,x);
print(ab);
return ab;
END;
then dmy()