Eating clean is pretty basic, it's just not having refined junk and artificial stuff. So not a lot (if any) of sugar, gluten, sweeteners etc.
This is what my diet typically looks like:
Breakfast: Porridge with water/unsweetened almond milk with a scoop of suitable protein powder
Snack: Tin of tuna with chopped veg (peppers, carrot normally)
Lunch: Grilled chicken breast/small sirloin steak with LOTS of salad and 150g rice/quinoa. Salad is dry or I put olive oil and balsamic vinegar on
Snack: Mixed nuts
Dinner: Turkey/white fish with steamed veg and sweet potato mash.
I make EVERYTHING from scratch, nothing is pre packaged (except the protein powder!)
Some people take it really far and cut a lot out of their diets, like fruit because of the sugar, dairy products etc. Personally I have fruit as a treat, and only drink water or a few cups of tea/coffee a day. But I think if you just don't eat the junk food and keep away from artificial stuff then you're good to go!
Great that you've started lifting! That's brilliant! A clean diet will compliment your training so much better than any "diet" food. It can be hard work but the results and health benefits are so worth it!