Sorry a real newb wanting a clarification. If the opening price...

Sorry a real newb wanting a clarification.
If the opening price on Tuesday is 4.5c for example does that mean all buy offers less than that are not processed? or still processed if there are sell offers below that.
Also there are 279 buyers but only a handful are shown, does that mean others are either less or more than what is shown on the screen there? So no one has a buy offer for 4.5c atm?
If so looking at the screen, if I make a buy offer at 4.5c I will get the shares??
Sorry for the obvious questions