So I create my mod in the geck wich is a companion mod. I open fallout 3, select it in the date folder, and then play and the companion is not there. Yes, I did place him in the world. Please help

Did you create a new cell where you placed your companion and not put in Navmesh? That will make NPC disappear and pop into unwanted locations. If you used default locations for your companion, verify your AI packages allow him/her to be where you expect at the proper times. You can check if your NPC is in the game by grabbing his Ref ID in the Geck and then using these two console commands:

prid XXYYYYYY

moveto player

(Note: XX represents the mod index of your mod as it loads into the game, the values start at 00 and increments as each mod loads).