Gravity question

Please correct me if I'm wrong. From basic understanding and education fax are, gravity falls is down to the center of the earth. And gravity also those with keeps the standing here and what makes it hard for plane to lift off from the ground. And as we go deeper into the ocean the pressure from the weight of Adam on top of us will crush us. And or force of gravity is stronger there with crushes us. Then please help me clarify why it's hard to get out of our atmosphere if the lower we go the more intense the gravity and or pressure? If what you're saying is true the higher in our atmosphere we go the harder it is to get out of and the lower we go in the ocean the more gravity or pressure, that what you're saying is zero point would be the surface of Earth? And this case none of the education that we've learned so far is correct we should be looking for a centralized zero point on the surface of the Earth. Logically, if anything we've been taught is correct, then it should be relatively easy to leave Earth by just going straight on our round planet, right? What is the surface of the Earth is our zero point, then gravity either does not exist or is completely different then what we've been taught.