Hey, it's more important now that we are gonna play the winners next season!
The way the playoffs work is explained in some detail here:
Winning your regional group of the Segunda B (there are four of them) is a good thing, as then you only have to win one round of playoffs to go up. This year it's our friends from Mirandés who play Atletico Baleares from Mallorca, while the other yellow submarine (Cadiz) take on Real Madrid's second team, Real Madrid Castilla. The winners of those matches (over two legs) are automatically promoted to the Segunda. I expect Mirandés to make it this time; the other matchup might be tight but I think both of the clubs involved will ultimately win through anyway.
The losers of these two matches combine with the six winners of these matches (two-legged ties, home and away) to make up a group of eight teams who play through, with the final two winning promotion:
CD Lugo vs SD Eibar
Some of these names should be familiar--Albacete and Ponferradina were only relegated from the Segunda last year, Tenerife has been a Primera side in the past. But then there is Huracán Valencia, a team which has no history whatsoever, precious little fan support, and no stadium. They were able to buy a spot in the Segunda B and, credit to them, have reached the playoffs. If they win through, well....
Some of these clubs--in fact, most--play in really small grounds. If you thought Mirandes's Anduva ground was small.... it would be fun though if RB Linense win through, because their ground is very close to the Rock of Gibraltar and has a helluva view! My money would be on the "Clockwork Cheese" of Albacete to make a quick return to the Segunda, and probably the loser of the Real Madrid Castilla-Cadiz matchup, with Tenerife as a wildcard choice.
Whoever wins through will replace VIllarreal B and (probably) Alcoyano, Gimastic Tarragona and Cartagena. Those teams drop to the Segunda B, but it may be a while before we find out the composition of Villarreal B's regional group (Segunda B, Group 3). This is because several teams went out of business over the course of the year in the Segunda B, and as Sr. Roig said, there is no middle class in Spanish football--either very rich, or very poor! So finding enough teams to compete in the Segunda B might not be easy.