If you're new to machines, just take a low amount of weight and see how the thing works.
For example: the regular and incline-chestpress machines in my gym provide 2 somewhat broad handles, which means I got quite some space to place my hands. Every position will train my chest differently. Try different positions and learn how they affect your muscle. Some machines are harder than others. Look at how other people are using them, you can learn a lot from that alone.
Machines that got cables can often be used to train multiple muscle-groups. If you can change the cable position vertically, you can often train biceps, triceps and even some lats and shoulder with just 1 machine. Again: see how other people use them and try things out.
As for free weights.. well they can be quite tricky... I was always performing a dumbell-press where I would have my hands against each other when my arms would be fully stretched, meaning my hands would move towards each other when pushing upward. I tried pushing them straight up instead of to each other (that would be the same movement as with a barbell) and my muscles started burning a lot faster, even with weights up to 10kgs lighter!
The gym can be intimidating when you're new around, but keep in mind that everybody started out with 0 knowledge. Exercises in the gym aren't rocket science and everybody can learn them, it's just that there's so much exercises that it might seem very complex.
Last but not least: never care how much other people lift!!!! I started out with dumbell presses as low as 6kg per dumbell, and now, after 1,5 years I don't see much people (apart from the beasty boys) lifting much more than me. Everybody will be outmatched some day. Even if you can lift 150kgs on the bench, there might come a guy around who does 160kg. Train for yourself for shere pleasure and results and focus on that.