Trump campaigned for months by demonizing undocumented immigrants, and he has continued his war on them since being elected. He wants to build a wall between the United States and Mexico (even though undocumented immigration is currently about a net zero -- with as many leaving as are entering), and he wants to deport those currently living and working in the United States.
He gives a couple of reasons for this. First, he claims they are criminals and boost crime in the United States. That's a ludicrous notion, since all studies have shown that undocumented immigrants have a significantly lower rate of committing crimes than citizens of this country.
Second, he claims those undocumented workers are taking good jobs that Americans would like to have. That's also a ludicrous claim. Most of the undocumented workers don't have the education or skills necessary to take good jobs away from American citizens. The jobs they are filling are back-creakingly difficult, dirty, sometimes dangerous, and very low-paying jobs that American citizens don't want. By taking these jobs, those undocumented workers are actually helping the American economy (and also help it by the money they spend and taxes they pay in this country). These people are a net positive in this country.
There is a group of immigrants that do take good-paying jobs in this country that citizens would love to have. They are the nearly half a million legal and documented immigrants brought to this country by corporations under the H-1B visa program. The offending corporations will tell you that they can't find enough Americans with the education and skills necessary for those jobs. They are lying. They bring in the foreign workers because they can pay them many thousands of dollars less than they would have to pay an American (up to 40% less).
Those foreign workers either don't mind working for less (because they have fewer opportunities in their home country) or they can't complain (because their visa would be revoked and they would be replaced by a different foreign worker). In short, these workers are being brought in because they can be abused easier than American workers.
What would Trump like to do about these H-1B workers who actually take good jobs away from American citizens? He wants to increase the number of them that can be brought in. This shows just how hypocritical Trump is about immigration. He complains about immigrants taking good American jobs, but demonizes the wrong group while encouraging the importation of foreign workers that actually do take the good jobs that Americans want.
Don't let Trump fool you on the immigration issue. He doesn't care about saving good American jobs. He's just playing politics with immigration, and feeding voter misconceptions to further his own ends.