the short answer
The barbell bench press is a compound upper-body push that trains the chest, front shoulders, and triceps. To do it well, lie back with your eyes under the bar, pull your shoulder blades back and down so your upper back stays tight against the bench, then lower the bar under control to the lower chest with elbows tucked - not flared - and press it back up. If you fix one thing, fix that tight, retracted upper back: it is the platform the whole press is built on.
This article is general technique education for coaches and clients, not medical or rehab advice - form is individual, and a qualified coach giving a live form check is the gold standard for getting yours right.