The confusing part starts after you get the ticket. What you need on the day, and how to behave.
Entry times, prohibited items and identity checks differ from show to show, and even between venues for the same artist. Having to check or discard something at the door almost always traces back to not reading the notice. Notices often appear after tickets go on sale, so check again a few days before. Notices are often posted on both the official ticketing site and the organiser's account, so checking both is the sure way.
Many shows verify identity, so ID is nearly always required. Phone batteries drain fast at venues, which makes a power bank effectively essential. Mobile reception can be poor at venues, so open your mobile ticket in advance or check whether it can be saved offline.
Professional cameras with interchangeable lenses are usually refused. Selfie sticks and tripods are often banned because they block views. Food and drink depend on venue policy, and some venues require large bags to be checked in. When unsure, leaving it at home is simpler. For items where the rules are unclear, asking the organiser's enquiry channel in advance saves panic at the venue.
The entry queue and the merchandise queue are different things. If you plan to buy merchandise, arrive much earlier, as popular items can sell out on the day. With assigned seating and no merchandise plans, there is no need to rush. What you intend to do decides your arrival time. Merchandise is sometimes also sold online in advance, so check whether you can skip the queue at the venue.
Blocking the view in front of you affects everyone behind. Even where filming is allowed, raised arms block the rows behind. Keeping walkways clear during the show and taking your rubbish with you afterwards is the basic courtesy. A light stick held too high can block views too, so waving it at about chest height is best.
Traffic around large venues gets extremely congested before and after a show. Check in advance when public transport stops running, and plan how you will get home allowing for the show running longer than scheduled. When it ends, crowds pour into stations and stops all at once, so waiting a little before moving, or boarding a stop or two away, are options. If you are travelling from far away, booking accommodation on the same line as the venue makes getting back much easier.
Concerts mean standing for a long time or sitting in cramped seats, and with the wait to enter it adds up to several hours. Eat before the show and bring water if it is allowed. In standing areas, keep an eye on your surroundings so you do not fall when the crowd surges forward, and if you feel unwell, do not push yourself — tell security staff immediately. Outdoor summer shows call for protection against heatstroke, and winter ones for clothing against the cold.
There is still a little to do once the show ends. When leaving, it is safer not to rush and to move slowly following staff directions. If you lose something, check the venue's lost and found or the organiser's notices, so make a habit of checking your belongings before and after. When posting videos or photos on social media, recheck the show's filming rules and, as a courtesy, avoid large shots of other audience members' faces.