Back in the Saddle

 is a quest in Fallout: New Vegas.

Quick walkthrough
After the character creation, Sunny Smiles asks you if you would like some training. This quest is optional, but if you choose to do it, Sunny gives you training. The quest involves some target practice, a brief hunt, and clearing three water wells of Geckos. Sunny will supply you with a varmint rifle and some ammo upon accepting the quest. At the final well, a woman is under attack. If you manage to save the Goodsprings settler being attacked, your standing in the community improves upon speaking to her afterwards and you will also receive x3 purified water. Once this final well is clear, you can talk to Sunny to be paid 50 caps for your help. Sunny will then ask you to go talk to Trudy before you leave. Talking to Trudy will complete this quest and you will be rewarded with 50 exp.

Detailed walkthrough
After setting up your character via the small tutorial inside Doctor Mitchell's house, he will direct you to the town saloon, stating that a woman named Sunny Smiles will be able to help you with your dilemma. Upon exiting the house, run forward towards the marker and enter the saloon. When you enter, you will be greeted by Cheyenne, Sunny's dog, and Sunny herself. She tells you that the Doc informed her of your coming and to meet her outback. Follow her, and upon reaching her outside, she will give you a Varmint Rifle and 50 5.56mm rounds. A shooting tutorial ensues, teaching you about aiming down the sights and crouching. After you shoot the 3 sarsaparilla bottles, she will then ask you if you would like to tag along on a little job. At this point, anytime you talk to her you can choose to end the tutorial, but for the sake of 50 bottlecaps, reputation and 3 purified water, continue the quest. You will then run south, towards the Goodsprings Source. Once you get to the first locale, Sunny will tell you to sneak, by crouching, to surprise the geckos. Once the geckos are dead, speak to Sunny and continue onto the next two wells. This part may be a little random, because sometimes two geckos are at the second spring while the other three attack the Goodsprings citizen, or all five geckos will be attacking the citizen. Either way, kill the geckos and talk to the citizen; she will give you 3 bottles of Purified Water and improves your reputation in good springs. Talk to Sunny afterwards, and she will give you 50 bottlecaps and the ability to start a side-tutorial about the Survival skill. If you choose to accept the tutorial, you must then head north to Goodsprings and find Xander Root outside the schoolhouse; there are Giant Mantis Nymphs around, so watch out. You must then head further north towards the Goodsprings Cemetery to pick up some Broc Flower. Be cautious, as there are Bloatflies in the area. Once you have both ingredients, head back to Sunny and talk to her. She will explain the uses of campfires and workbenches. Once you finish talking about the Survival skill, you will be directed to Trudy, who runs the saloon. The quest ends once you speak to Trudy. Congratulations! You now know the basic mechanics of combat in Fallout: New Vegas!

Bugs
It is possible for the mission not to complete even after following all of the dialogue options with Trudy at the end of the quest. After talking to her she just remains behind the bar and the mission remains active. This also seems to affect the start of another quest in Goodsprings: Ghost Town Gunfight.

It is possible for the mission to not continue automatically. if a random critter appears outside the saloon when you follow Sunny and she moves to attack she will not give you the rifle or the mission unless you push her back to where she was standing when you come out of the saloon

Reference
The quest name is a likely reference to the 1941 Gene Autry cowboy film, "Back In The Saddle". There is also an Aerosmith song 'Back in the Saddle', released in 1977.