Company work-out challenge

First, let me say, i was never one growing up to work-out in a gym. Instead, i played team sports, and then in high school, into college and even after, did individual sports and hobbies like rock climbing, swimming, mountain biking, motocross, etc.

I work in the aquatic industry, hired by HOA communities to hire lifeguards and do all work associated with running a pool year-around. Part of my job is to teach lifeguards how to save lives. Being in a pool is something i do a lot in the spring and keeps me in shape, some what.

Now that its winter, it's slow at work and the upper management have a lot of time to relax with family. Instead of wasting away on a couch, we came up with a work-out challenge.

Challenge: Work-out a minimum of four times a week, no less than 30-minutes each session. In a group text, send a picture and description of work out. If you don't make the four work outs, you have to donate money to a charity that you despise and post the donation to social media so everyone can see.

So far, for two weeks, i've only made the minimum and haven't done more than 4 a week, but have gone longer than 30-minutes.

My goal is to loose about 15-pounds in december and january. At the gym, i have stationary equipment and free weights.

What kind of beginner work out plan would you guys recommend for core parts of the body? Arms? Legs? Core? Chest? Back?

Super new to the guy, so i've used elliptical, cycle bike, and free weights and haven't noticed a change yet.