Can I use p265 70 r18 to replace p265 70 r17 tires?

No. The last number refers to the rim diameter. You would have also buy 18 inch rims in order to use the 265/70R18 inch tires. Also these would likely be bit tall. If you bought 18 inch rims the correct size would be 265/65R18.

P = speed rating up to 94mph.

265 = tire width in millimeters.

/70 = the aspect ratio between width and hight, the hight of the tire from rim to tread being 70% of the width or 185.5mm.

R = radial ply tire.

18 = 18 inch diameter rim.

17 = 17 inch diameter rim.

Actually, of all the above numbers it's the rim diameter that has to be exactly the same. For an example, you could probably fit 245/80R17 or 285/65R17 tires on your rims, but changing the 17 for an 18 just won't work. Sorry!

No, they indicate the size of the rim, and an 18" tire cannot be installed on a 17" rim, there would be a gap between the bead of the tire and the wall of the rim.

the first number in a tire size is the width in MM, the second number is the ratio of the sidewall height in comparison to the width and the 3rd is the rim size in inches.

So your tires are 265mm wide, the side wall (distance from where the tire and rim meet to where the tread starts) is 70% of 265mm and it is mounted on a 17 inch rim. The first 2 numbers can usually be be upsized or downsized, but its not usually recommended as most modern cars are designed for the stock tire size.

You can increase the size of the rim if you buy new rims, but typically the tire size will change to accommodate the increase in rim size, i.e. bigger rim means you need a smaller side wall so the overall diameter of the tire does not change dramtically

Physically impossible. Only a 17 inch diameter tire will fit on a 17 inch diameter rim.

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R means Radial and 18 is the diameter of the wheel. You cannot use 18 inch tires on a 17 inch wheel.