The President is selected, not by a direct vote of the people, but by the Electoral College. When citizens go to the polls, they select who the members of the Electoral College will be.
There are 538 members of the Electoral College, called Electors. Each state gets one Elector for each Congressman and Senator. Texas has 34. Only California has more (55).
Some states have laws that require Electors to vote for the Presidental candidate with whom they are associated. Texas does not have such a law, meaning that Electors are not required to vote for a specific candidate.
In 48 of the 50 states (including Texas), the presidential candidate who wins the most popular votes within a state wins all of that state's electors. Nebraska and Maine are not winner take all states. To become President, a candidate must get a majority of Electors or 270.
Presidential campaigns develop strategies to win 270 Electors. States that are not friendly to their party are often skipped as are states that they assume they will win. This is usually based on history. Texas is considered a safe Republican state because a Democrat has not won Texas in more than 30 years. The last Democrat to carry Texas was Jimmy Carter in 1976.
Candidates focus their attention and money on battleground states. These are states where neither party dominates.
The National Register adminsters the Electoral College, and its website has an Electoral College Calculator where you can predict election results by state and see who would win.
A private site has an easier-to-use U.S. map where you can also create your own Presidential predictions. Click on a state to change it from a red state to a blue state to a toss up state.
The National Register also has information for teachers.
You can also look up Electoral College results throughout history all the way back George Washington's first Electoral College victory in 1789.