The charoset is the sweet paste eaten at the seder, and its stated purpose is a visual one: it is made to resemble the mortar with which the enslaved Israelites laid brick.
Sweetness for hard labour
The charoset is a paste of fruit, nuts, spice and wine, sweet and thick, into which the bitter herb is dipped before it is eaten, and the Haggadah explains it as a reminder of the mortar the Israelites used in their forced labour in Egypt, so a sweet food is given to recall hard bondage. The pairing is deliberate: the sweetness set against the bitterness of the maror it accompanies, and the pleasant taste against the harsh thing it represents, which is one of the small paradoxes the seder builds into its symbolism.
Many recipes, one meaning
The charoset is one of the foods that most varies between communities, the fruits and spices reflecting local produce, so that the pastes of different Jewish traditions differ widely in their ingredients while agreeing in their purpose and their appearance. That variety makes the charoset a marker of community and origin as much as a symbol of the mortar. It has no independent blessing of its own, serving rather to temper and to accompany the bitter herb, and its function within the seder is fixed by its resemblance to the mortar and by the dipping of the maror into it, so that the memory of labour is present in the sweetness as well as in the bitterness of the night.