Question: Are we supposed to dip our bread into salt every time we eat, or only challa on Shabbos?
Answer: The Gemara (Berachos 40a) teaches that one should not say hamotzi before eating bread unless one has salt or other dips in front of them. Rambam (Berachos 7:3) writes that this applies unless one intends on eating dry, plain bread. Likewise, the Shulchan Aruch (OC 167:5) writes that if the bread was already flavoured or salted, there is no need to have salt at the table.
Nonetheless, the Rema quotes the Beis Yosef who writes that our tables are compared to the mizbeach, and our eating to the korbanos. As such, we should always have salt on the table with bread, just as the korbanos were all salted. The Mishna Berura (167:30) explains that when one shares one’s bread with the poor, one’s ‘table’ atones for their sins in place of the korbanos (See Berachos 55a).
The Magen Avraham (167:15) writes that even though our bread contains salt, there are kabbalistic reasons for why we dip our bread into salt. The Mishna Berura (167:33) adds that according to kabbala, one should dip their bread three times into salt.
In conclusion, as our bread is flavoured, there is no obligation to dip it into salt. Nonetheless, there are different reasons why one should still try to do so.