Herealways Pieces are a new currency that was introduced to Destiny 2 in Beyond Light. While it is new to the game, it has been floating around in the lore for quite a while.
Herealways are a Fallen currency, and Variks wants to trade for them at his little hideout on Europa. You won’t be able to earn them until after you have finished the Beyond Light campaign, and have complete the first sabotage mission for Variks.
It is a long mission where you need to infiltrate a factor that the Fallen are using to build Brigs. You need to sabotage the Brigs, then sabotage the main factor itself.
After that, return to Variks and you will be able to do smaller Sabotage missions, which he will sell to you in exchange for Herealways Pieces. To actually earn the Herealways Pieces, all you need to is complete activities on Europa. Lost Sectors, Patrols, Public Events and even killing enemies can all earn you Herealways Pieces.
Once you have enough, you can bring to Variks and hand them in for a Sabotage mission. The missions are broken up into three tiers, and completing them will net you some bonuses. For example, the very first mission will increase the rate at which you earn Herealways Pieces for the first 30 that you earn each day.
The cost of the missions varies between the tiers, and they get more expensive as you go up in tiers. The missions themselves also become tougher, but this shouldn’t be an issue as you Power increase throughout the season.