I can see how Tapas culture can be a bit intimidating for foreigners, but I hope I can demystify it a bit for you :)
What is a Tapas bar? Tapas bars are places usually located in the more touristy centres of cities in Spain that will have long bar tables with different tapas on top, here you usually make your way to the bar first and talk to the bartender directly to get service or if you want a check, waiters will not come to you here, you have to be more proactive. I've seen many "tapas bars" in foreign countries (cashing in on the tapas brand) but they never come close to the actual tapas experience in Spain.
What is the "rhythm of tapas"? Firstly don't expect that the tapas are all small or cheap, often foreigners are surprised when their tapas order comes and they found they have over ordered and overpaid. Take it slow and pace yourself, order 1-2 tapas at once then if wanting more order another round of 1-2 or move on to the next tapas bar. Also know that there are Tapas and Raciones, Tapas are small plates to share between 1-2 people while Raciones are larger portions of food that are meant to be shared by a group of people.
What is the "architure of tapas"? Usually there will be a bar with a glass cover so you can point to what tapas you want. At the bar there are bar stools so you sit on those while eating, your plates will actually be on the bar table. Don't be "patient", you will have to compete for the bartender's attention with others at the bar, don't be afraid to raise your voice if they are not coming to you, this comes naturally for local Spanish but may be difficult for first timers from abroad. Once you start ordering tapas they will keep an open tap for you until you order the check.
In Barcelona, the better Tapas bars tend to be around El Born and El Poble sec neighborhoods, I can recommend Bar Celta Pulperia and Quimet & Quimet, respectively. But you got to go out and explore, avoid places where they have the menus in English first and all the patrons are foreigners, these days that is hard to do in Barcelona cause of overtourism.