Generally, you have to use your Repair skill on the tiny forcefield emitter to temporarily disable it. This works on yellow fields. You can pass through red fields incurring damage. Or you can use explosives.
In some cases you can use items like computer terminals or power switches (like in S.A.D.) to turn off force fields or power them down so they become 'red' and passable. This can, I think, somethimes be done in dialogue too (vide Hubologists.)
There.