The problem is this, like two days ago i check the coolant tank and there was a very strange liquid but i keep using the car as normally i do but today in the night I realized that in the ground was some of this liquid, I believe that it is oil what could be happening?? why the oil passes to the coolant tank??? i do check the oil of the engine and it is quite normal, THE CAR WORKS NORMALLY AS EVERY DAY DOES NOT HAVE ANY PROBLEM

can some one help me please???

 

What does the coolant actually look like? "Strange" doesn't really help.
Is it "milky", like a milkshake? If so, what color is it? Brownish? Redish? White-ish?
You could have engine oil(brown milkshake), or transmission fluid(red milkshake) in the coolant. Engine oil in the coolant could be from a bad head gasket, a cracked head, or a cracked engine block.
Trans fluid in the coolant would normally indicate a ruptured trans cooler, located inside of the radiator. If the trans cooler is ruptured, you will also be getting coolant into the trans. You should check the trans fluid for coolant contamination. Transmissions do NOT deal well with coolant. If there is ANY coolant in the trans, the trans will need to be removed, and completely rebuilt.

More info is needed.
How long have you had the car?