Guillen joined the Giants on Saturday, one day after being acquired with cash from Kansas City for a player to be named.
"I like to win," he said. "I'm a very passionate guy and I love to win. I hate losing. This is a great opportunity. I'm very motivated. I'm the type of player who likes this atmosphere, a playoff atmosphere and winning. I'm very excited."
San Francisco enters the day 3½ games behind San Diego in the NL West and on top of the wild-card standings.
The Giants are counting on Guillen to provide a boost the middle of the lineup for the stretch drive. He was batting .255 with 16 homers and 62 RBIs before being designated for assignment by the Royals on Aug. 5.
The Giants will wait a day to get Guillen into the starting lineup. He didn't arrive in San Francisco from Florida until about 11 p.m. Friday night and manager Bruce Bochy wanted to give him a day to get acclimated to his new environment.
Bochy said Guillen was available off the bench Saturday against San Diego and would start Sunday's series finale against the Padres.
"It's pretty tough to travel that far and face a tough right-hander," Bochy said. "We'd like to give him a day to settle in to get to know the ballpark and take some fly balls. I'll have him available off the bench."
Guillen has had his share of issues during his career and is now joining his 10th major league franchise since entering the big leagues in 1997 with Pittsburgh.
He was suspended by the Angels for the last two weeks of the 2004 regular season and postseason for inappropriate conduct after expressing his displeasure with manager Mike Scioscia. After the year, Guillen was traded to Washington.
In July 2008, Guillen got into a heated clubhouse exchange with Royals pitching coach Bob McClure, knocking over chairs before several players separated them before a game at Tampa Bay. Guillen also unleashed a profanity-filled tirade against his teammates that May.
Guillen said he doesn't envision any problems fitting in with the Giants.
"I'm a veteran," he said. "I just have to come and contribute and play and produce. That's the reason they brought me here. If I don't produce, I won't play. When you're in a pennant race, you try to put you best nine players you have out on the field."
The 34-year-old Guillen signed a $36 million, three-year contract three years ago that made him the Royals' highest-paid player per year in team history. Kansas City is paying the bulk of Guillen's salary for the rest of this season.
Guillen struggled with injuries in Kansas City. He played in only 81 games last year and hit nine homers, tied for his fewest since 2002. He was out for weeks after injuring his knee while he was putting on a shin guard and missed several days of spring training in 2009 after deciding to rip out an ingrown toenail with a pair of pliers.
Guillen had struggled with a left quadriceps injury this season and ended his career in Kansas City in an 0-for-21 slump
"Kansas City is in the past. I'm in San Francisco now. I'm just here to win," he said. "I was having an OK year but I was dealing with some injuries. It's tough to play when you're hurt. I'm healthy now. It's all good."
The Giants optioned infielder Emmanuel Burriss to Triple-A Fresno to make room for Guillen.