First of all, relax. Its not about nutrition at this age, its much much less stressful if you stop worrying about what baby is eating, as milk should be the main form of nutrition for some time to come, and just have baby sitting with you when you have something to eat.
At 6 months you can start putting a couple of pieces of food - broccoli, carrot, chicken strip, banana etc - on the highchair tray and leave them to copy you, or not, or throw the food, gum it, spit it out, eat it occasionally. Make the food big enough to hold in a fist with a bit sticking out the top and let baby have fun.
If you are spooning food then offer the spoon, let baby decide if they want it in their mouth or not, be led by baby.
When they've had enough its fine. Just leave them to play until you've finished.
Oh, and it can sometimes take til between 9 and 10 months old to get the hang of it. As long as they still have milk there is no problem at all.