An oblique tip is cut at an angle, which is usually about 15 degrees, normally from top right to lower left. This is called a left oblique. When the angle is from the top left to the lower right it is called a right oblique.
The oblique's line-width variation is more subtle than the distinct broad down-stroke and narrow cross-stroke achieved with an italic or stub. The broadest stroke for an oblique is on the diagonal, giving your penmanship an understated character.
The key to using an oblique nib is in the rotation of the pen in your fingertips. If you are right-handed you will rotate the gripping section of a left oblique, and thus the nib, toward your thumb. This will keep the flat edge properly on the paper as you write. If you're left-handed you will use the same left rotation of the gripping section toward your pinky finger. When using a right oblique, the opposit is true with the gripping section rotated to the right in your fingertips.