Most elementary particles (like electrons and quarks) have an intrinsic property called spin which, when on charged particles (again like electrons and quarks) produces a magnetic field. However, this field is usually very weak, since the orientations of many such particles cancel each-other out. The earth has a magnetic field created by convection currents in the outer core, which is made of molten iron (plus a few other elements as well). Any particle in this field will experience its very slight magnetic field, but it is so weak that it is difficult to notice without a fairly sophisticated measuring device like a compass made out of material that is easily magnetized (like iron).

There are some neutron stars (called magnetars) that do have magnetic fields so powerful they would tear you apart if you got close due to the diamagnetic effects of the fields on the water in your body. However, the earth's effects are so minor that it doesn't matter. The only meaningful force you experience from the earth is gravity.

Not every atom is affected by the earth's magnetic field. Whether or not an atom is affected depends on how its "electron configuration" (how many electrons is has, and how they are distributed in the atom). Let's take an element whose atoms are affected by the magnetic field, for example, iron (Fe). No matter where on earth you put an atom of iron, it will be vaguely affected by the earth's magnetic field. This is because the earth's magnetic field is equally strong all over the globe. We take advantage of this when we use a compass to navigate -- you can use a compass anywhere on the earth and it will always point North.