If you didn't realise it when you started your journey to Catalunya you will certainly notice that many things are rather odd and confusing when you arrive in Catalunya. There are flags everywhere that definitely aren't Spanish and most people are speaking a language that you won't understand even if you are proficient in Spanish. In other words it is not a dialect but an entirely separate language. The history of Catalunya and Spain is long and complicated (There is a good summary at Wikipedia for the interested). Suffice to say that they were independent and powerful seafaring nation that eventually ended up as part of Spain. Napoleon also messed things up for the Catalans and snatched the bit of Catalunya that was on the French side of the Pyrenees (Oddly there is still a Catalan city called Llivía situated inside France). In recent history the Spanish Dictator Franco was not a big fan of Catalans and their culture and did his best to remove their cultural identity and make them part of Spain. Somewhat obviously, this had the opposite effect which probably to a large extent explains why there is such a strong independence movement in Catalunya today.
Without being linguist experts we would describe Catalan as some sort of mixture of Spanish (Castellano) and French garnished with a bit of Italian. The Catalans are very proud of their culture and language and Catalan is taught at school as the first language but most if not all Catalans also speak Spanish fluently. As a visitor in Catalunya you will notice that almost all signs are printed in Catalan and Spanish, at restaurants you can choose between the Catalan and the Spanish menu, there are TV channels only in Catalan etc.
Politically, the Catalans are split in two major groups. One group wants more autonomy and better deals for Catalans (Catalunya is an economical powerhouse compared to much of the rest of Spain and they believe they are being treated unfairly). The other major grouping wants complete independence from Spain. Basically, their aim is to form the republic of Catalunya. The country is roughly split 50:50 between these two groups although the independence movement seems to gather momentum as a consequence of the financial crisis in Spain that has made life difficult for Catalans.
There are many Catalan flags that you will see all over Catalunya, however three flags dominate the picture:
Le Senyera, is the official flag of the province of Catalunya:
Estelada, is the Independence for Catalunya flag:
Països Catalans, is the independence for all Catalan speaking provinces flag, which includes, Catalunya, Valencia, the Balearic Islands, Alghero (Sardinia, Italy) and Rousillon (France):