Texas became deregulated in most areas back in 2002. This gave consumers like you the option to shop multiple rates and companies to be your provider versus being stuck with only one provider option.
Although this opened the door to tons of savings for consumers, it also allowed Retail Electric Providers to determine their own rates and offer not so transparent plans that can trick you into thinking you will be saving money, when in reality you will not.
Electricity billing can be a bit confusing. Ultimately, you are paying 2 providers. You will have your chosen Retail Electric Provider which does the resell of electricity at a certain rate based on the plan you selected.
You also have Transmission and Distribution Utility (TDU) which is typically going to be either CenterPoint or Texas New Mexico Power. You have no options when it comes to who your TDU is or their fees. Every resident in the designated area will pay the same regulated delivery charges each month.
A fixed rate is when a contract between the Retail Electric Provider and the consumer have agreed to a set rate for a certain time frame. These plans usually run anywhere from 3 months all the way up to 3-5 years.
A variable rate is a month to month plan where the rates will vary based on the wholesale energy cost. There are many other factors that can play into this pricing, all of which are determined by the Retail Electric Provider.