These additional points elaborate on what ETD said in his reply.
A Swiss Tournament is one in which you are matched against opponents so that the pool of players is differentiated as much as possible in as few rounds as possible. So, in the first round, those in the top half of the pool by rating are each paired against someone from the bottom half. The assumption is that the higher-rated player will win each game. In the 2nd round, the winners of Round 1 play each other, and the losers play each other. As points accumulate, the process continues until, at the end, the players with the best scores play each other in a few (hopefull) decisive matches. The winner has thus had the toughest opposition, while others are quickly sorted into the level at which they will get a succession of fair games. SS tourneys are usually between 4 and 9 rounds, so while each of the 120 players will each only play a maximum of 9 other players, the SS allows a definitive winner to be selected.
"Sudden Death" means that the first player whose time runs out (i.e. his "flag falls") at the end of that time control instantly loses the game. This is known as "forfeiting on time."
d5 does mean that there's a delay in the way the timer works. There are several kinds of delay. The most common is the "simple delay", in which the clock counts down the seconds of the delay. If it reaches zero, then the time control allotment starts running down. So, if you had 20 minutes after your last move, and a 5-second delay is in effect, then when the opponent punches the clock, the timer will count down from 5 to 0, and then display 20:00, then 19:59, and so on. If you make a move and punch the clock after 3 seconds (i.e. the delay timer displays 2), one of 2 things may happen: a) your original time of 20:00 is displayed and the opponent's delay timer starts, b) the remainder of the delay is added to your time, and the clock shows 20:02 for your time. The second approach is common on ICC and in many digital clocks. A 3rd method is occasionally used, as Bobby Fischer proposed it: The delay is handled as an increment, so that when your clock is punched it reads 20:05, not 20:00 as it did after your prior move. You get to keep any unused increment. A 4th method is also possible: Your time reads 20:00 when your clock starts, but after you make your move and punch the clock, the increment is added retroactively. So, if you started at 20:00 and took 30 seconds to move and punch the clock, the clock would read 19:30 just before you punched it, and 19:35 just after. The retroactive increment was invented to make sure that players who are low on time won't be able to play indefinitely unless all of their moves are made in 4 seconds or less. Finally, some controls require that the clock's total never exceed the original time control allotment. Otherwise, a player who played every move in 4 seconds or less would be able to accumulate time indefinitely, and always have more than the time control amount, in some situations, unless this condition were imposed. That's why it was invented.