When a voter goes to vote, he/she has to know which polling precinct to go to and has to have a valid ID proving he/she is that voter, before he/she can vote. You do not just walk in anywhere and vote.
Marcella, you are referring to TEXAS law and election procedure, with which you are very familiar. Texas's system is among the best in the country in terms of limiting fraud and cheating, which may be why Democrats haven't won statewide elections in Texas in quite some time.
However, in other states, procedures are much more lax, so elections are much more prone to all kinds of "irregularities." Therein lies the likelihood of prospective fraud and cheating schemes by the Clinton machine in the 2016 presidential elections.