When speaking to an audience about God I have asked, "How many of you have seen the leader of our country?" Most hands go up. When I ask if they have seen him or her in person most hands go down.
What we have seen is an energy form, light, that comes from the television. Unlike God, the leader's body cannot generate visible light. So energy (light) from the studio lighting is bounced off his body and captured in the camera. It is there changed to electronic energy to be transmitted as radio wave energy to a satellite, etc. It is sent through the air, arrives at your television and is transformed back to visible light for your eyes. And because these radio waves have "intelligence" on them, behold, the country's leader is everywhere, in your home, across the street, in the next state, around the world. If you go into the television or electronics section of any major store the leader might be in dozens of places! Yet, he literally is in one place.
Now, like God, the leader can generate an energy form called sound. Voice sound is the compression and rarefaction of air by the vocal chords. Like the video, this energy is changed at the microphone and transmitted to our television. The leader's image speaks. Likewise, the Father is in one place at one time. But he is everywhere through the power of his spirit ("the power of the Highest" as it is stated in Luke 1:35). His spirit reaches out everywhere he wishes it to go and enables him to do mighty works anywhere as he wills.
No, God is NOT everywhere at once, but in one place only. In fact, he does not appear to even have his eyes constantly watching every thought, choice and action that humans make.
After hearing about Sodom and Gomorrah's horrendous sins (from angels, who are his messengers), God felt he needed to see FOR HIMSELF if the two sinful cities were as dedicated to doing evil as was reported to him. He personally told his friend Abraham that he MUST go down and see for himself whether the accusations of sin and rebellion were true or not (see Genesis 18:20 - 21).
In conclusion, our heavenly Father is one being who is not everywhere but is in one place at one time. Jesus Christ, who is also God, is like the Father in that he, too, is in one place at a time.