The AFU stands for Armed Forces of Ukraine. These artillery shells would be targeting Russian soldiers.

Edit: I think all the replies are referring to the fighting in the Donbass and Lujansk regions between the Ukrainian military and unpopular separatist groups who had Russian backing. To be clear, they were unpopular locally and had to seize power by force and shut down media and communication networks to make it harder to voice opposition. The Ukrainian military wasn't interested in killing civilians, they were interested in freeing them from the militias that took over the areas. The hostile takeover started when Russia invaded Ukraine in 2014. Those militias eventually began to fill with actual Russian soldiers, though the exact highest fraction is unclear. Russia claimed that, if there were any Russian soldiers there, they were independent volunteers.