So I joined the gym

[eyestightshut]

Have signed up to our local gym. My aim is to lose weight, but more importantly, tone up, as I look like I am melting from the neck down.
Obviously I want all of this to happen in about 5 minutes to make the time I spend there as productive as possible. I am not unfit (I can run 5k in about 30 minutes) but am weaker than a very weak thing, particularly around what is supposed to be my core muscles - I appear to have been born without any, hence the melty look Please can you give me your top tips to shape up in as spedy a time as possible?

[Superherosidekick]

HIIT, Grit - basically interval training, either a class or a program put together for you. Alternate with weight training and some cardio classes.
A trainer at the gym should be able to put together a core strengthening program for you or try Pilates for core building.