Alt-Right is a large group of people that includes Neoreactionaries, 4-chan wizards, and, yes, some racists--but not nearly as many as the Democrats. What the Alt-Right believes is that Western Culture is worth preserving and that liberals are trying to dismantle it. Their tools are:
Diversity: This is an attempt to undermine the genetic component of Western Culture under the guise of promoting the idea of equality (the opposite of 'quality').
Social Justice: This is an attempt to destroy all recognizable elements of Western Culture using the method of making them retroactively racist, privileged, or problematic. These are all impenetrable code-words that shift meaning when you ask for a definition--but they all mean "bad." People trying to keep up with political correctness will quickly come to discover that it's impossible. No matter what you did yesterday, today it's racist (or whatever).
Mob-Rule Democracy: The Alt-Right understands that the liberal forces will inexorably use their influence in the media and the tool of inflicting shame to take over any nominal democracy.While it may sound authoritarian, the Alt-Right understands that if Western Culture is to be preserved, strongmen with the right moral fiber are needed.
Feminism: The liberals are using the "radical notion that women are people" as a cover for dismantling Western Socialization. There used to be men's areas and women's areas--today the latter is acceptable, but not the former--and even bathrooms are to be integrated. The Alt-Right understands that different biology (whether it be genetic heritage or gender) means a different society. They rightly reject Feminism, recognizing meaningful differences in the sexes.
Emotionalism: Liberals, having to appeal to females as primary shock-troops, have embraced the false-equality of emotional decision making vs. rational decision making. Thus they promote women to CEO positions (where they fail again and again) or to the Supreme Court (where they vote en bloc, always, with the liberal males). Alt-Rightists of the Neo-Reactionary-sub-type especially pride themselves on logical, clear-headed decision making.
You can start to see how the above would make Trump appeal to the Alt-Right--but is he actually Alt-Right?
Yes. And Thank God. While labels are always dangerous since as soon as there is a label a lefty will use it to commit bad behavior in the name of their enemy--but regardless, it is clear that Trump hits all the above markers:
He will dramatically reduce MENA immigration and South American infiltration into the US.
He spits in the face of Political Correctness and draws fire from all Social Justice Warriors.
He is a strong-man and will build a strong country. He has said so himself. Other authoritarians respect his obvious strength.
Women--especially liberal ones--have problems with Trump. For the actual feminists, they literally hate him because he is not susceptible to their attack. For others, they have been programmed since birth to believe that if treated "like a lady" they are being disrespected. What Donald Trump fits is the model of a gentleman.
Rationalism--Trump is carefully rational, refusing to make snap decisions and relying on common sense over base emotion. The women he employs in high-ranking positions are noted for their rationality.
On the other hand, is the Alt-Right racist?
No. The Alt-Right is race-realist. Understanding that other nations, other races, and other cultures don't have America's best interest at heart is simply understanding the way the world really is rather than the way (Liberals) want to make you think it is.