In 2d games traditionally there is something called "footsies". Footsies is a poking to gain advantage.
Usually a character has a range at which she has an advantage at over another.
IE Parasoul vs Fillia: Parasoul wants to keep Fillia at the tip of her umbrella moves since at that range every normal Parasoul uses beats Fillia's. Parasoul wants to keep this up until she can land a hit confirm into a combo (something like lp,mp,hp,hp). Fillia on the other hand is trying to get inside Parasoul's umbrella range once there she can use her short but +frames on block moves clp is +6, clk + too but don't remember exactly.
Fillia will do this by trying to punish a wrong move by Parasoul. If Parasoul gets in the habit of throwing napalm shot at a certain range or situation. Then Fillia can guess that and jump over or slide under the shot to start her offense. Fillia can also try to bait and whiff punish by dashing in and out of Parsoul's range.
Assists kind of blow all that up but should be thought of another extension to it. They are just extra moves for the point character. If Fillia has Double Butt assist then her range and options for attack go up exponentially. She can call Double outside Parasoul's normal's range forcing Parasoul into defense.
Most offense in SG is started by throw out an assist as a poke. If Double Butt assist hits try to hit confirm off it or try to gain a positional advantage. A counter to that is calling an assist in defense, ie Napalm pillar, to punish.
As a solo (don't play solo it sucks) you have to be very defensive. Try to bait out the assist by jumping in while blocking. If you play fortune like your tag says use your air mobility to dance and bait out bad moves from the opponent. And watch @
KhaosMuffins Fortune guide.
Does this help or make any sense? I don't know anymore.
Do you have more specific questions?