How do you open with 6 Clubs and 5 Spades?
The answer, as so often happens, is that it depends. If you have the 17 points to reverse, if necessary, you can open 1 Club, then rebid Spades, then rebid Spades again. The rebid of your second suit promises a 5-card suit and your opening 1 Club promises a 6-card suit since you didn't open your 5-card major.
If you have the 15 points for a 3-level reverse, if necessary, you can open 1 Spade, then rebid Clubs, then rebid Clubs again to promise 5 Spades and at least 5 Clubs.
If you lack the points for any reverse, you can open 1 Club and, if partner responds 1 No Trump, have to rebid Clubs or pass, not being able to show your Spades at all.
You can also choose to open 1 Spade and, if partner responds 2 Diamonds or 2 Hearts, have to lie with 2 Spades or 2 No Trump, not being able to show your 6-card Club suit.
You can see that the opening depends on your overall strength, the relative strength of your two suits and your taste for risk. The important lesson is that you should never open without considering your rebid.