When I first tried to understand idolatry I thought of the literal version:
a person worshiping a little statue asking it to bring rain, fertility, success, etc. etc.
To some people in this scenario might seem a little ridiculous. I know it seemed a little ridiculous to me
I mean, how can a tiny little figure have that kind of power? While it's possible that someone might pull out a statue of a deity and ask it for a new car, there is a more likely type of idolatry that we can fall prey to.
The essence of idolatry is attributing power to something that does not have such kind of power.
Idolatry began with worshiping nature. I heard that it started with the thought that even though there is G-d, He has "ministers" that should be thanked for doing their job. For example, since the Sun brings light, what's wrong with thanking the Sun? But this easily becomes thanking the Sun without realizing that the Sun's light is actually from G-d. Then it can slide one step further: if you don't thank the Sun, the Sun will stop shining for you, and you will suffer from lack of Sunlight. So, if you want Sunlight, you need to worship the Sun.
With idolatry there is commonly the situation of "getting the cookie". If you worship <insert deity here> you will get what you want. Doing something for a reward is routed in selfishness.
So how does this apply to today's world? Let's say you want a promotion at work because it will give you enough money to buy a new sports car. So, you believe that your boss holds the power to your promotion and the way to get your sports car. There is an important work function that your boss wants you to attend on the same day as your brother's wedding. Your boss dangles the carrot of a promotion telling you that you need to attend the work function if you want to be considered for a promotion. So you skip your brothers wedding. This is essentially idolatry.
1) You are attributing complete power to something other than G-d. If you are working hard and G-d desires to give you more money, G-d will do so the way He decides. You should ask G-d for more money rather than believing that your boss is the ultimate decider of your wealth.
2) Your focus is on "getting the cookie" rather than doing the right thing.
Idolatry can easily be used to justify selfishness.
The economy is bad, and my money is tight, so I'm not going to have any children.
(I don't believe that G-d will help provide for my family. I believe in the economists and would like to keep my two vacations a year)
I have to make other people look bad at work in order to be successful.
(I don't believe that G-d is One and is everywhere. I believe that the industry/society sets our measures of what is ethical at work)
I know I'm married, but I have an "agreement" with my spouse that we can have some fun on the side as long as we are open about it. We decided it's ok because it's between consenting adults and scientists proved that humans (who are essentially like animals right?) by nature are not monogamous.
(I don't believe in G-d's plan for humanity. I believe in the scientists who can determine what is moral behavior for humans.)
If I get people to believe in <insert deity here> I will be rewarded in heaven with riches and beautiful women. If I don't believe in said deity, I will experience an eternity of suffering.
(I don't believe that G-d teaches selflessness. I believe that <insert deity here> is important to worship because if I do whatever I'm told I will get lots of rewards.)