That is the same question I was asking at age 13—and am still dealing with it to this day many decades later. I have even acted in a motion picture about a boy who was stumped by the same question (Indescribable, 2013). 

To love God feels the same way as it does to love your father and mother or any other important person in your life—which is to say, sometimes it feels warm, sometimes cool, and sometimes it doesn’t feel at all but is just there. The big difference is that, since God is invisible, we have to believe in him without seeing him in order to love him. 

But that’s not as hard as it may seem at first, because he reveals himself in many ways that show he is real. He reveals himself in his created universe and in all the world around us. Christians and Jews together believe that God has revealed himself in mighty acts in history and in the words of the Law and the Prophets. 

The very command to love him that you quote is the call of God, a revelation of his desire to have a personal relationship with us. But he calls for the love above all other loves because God alone is God, and only God has the right to it. Christians believe that God’s highest revelation of himself and his love came to earth in the person of Jesus Christ. “For God so loved the world that he sent his only Son into the world, that whoever would believe in him should not perish, but have eternal life.” (John 3:16)

Love then is a drive inside us that wants to give (rather than get) which causes the lover to humble himself and submit himself to his beloved in order to serve his beloved. You can serve someone without loving that person—for pay, out of fear, for fun—but you cannot love without serving. Ultimately to love God is not about how it feels, it’s about what you do, whether you will lay down your life in loving service to God through doing loving service toward others (You shall love your neighbor as yourself). Jesus said that all the law and the prophets hang on these two commands.

I hope that helps.