A Spaniard is a person from Spain. That is the whole meaning — but the interesting part is when English speakers actually reach for this word instead of saying "a Spanish person", because they are not equally common.

In everyday talk, most people say Spanish, and they use it as an adjective: "my Spanish neighbour", "she's Spanish". Spaniard is the noun, and it shows up mainly in news writing, sports reporting and history books — "the Spaniard won the final in four sets", "the Spaniards arrived in 1519". In sports especially it is a handy way to name a player again without repeating their name.

Countable, so it takes a and a plural: a Spaniard, two Spaniards, the Spaniards. Capital S always.

Here is the part your textbook may not tell you. Nouns like this one — words that name a person by their country — are not evenly distributed in English, and some of them have picked up an unfriendly smell over the years. Nobody objects to Spaniard, and you can use it safely. But the same shape appears in words that people now avoid, and the safest habit for a learner is the adjective: "He is Spanish" is never wrong, never cold, and never risky. Save Spaniard for when you need a noun.

One more small thing worth knowing: people from Spain do not all feel equally Spanish. In Catalonia and the Basque Country, many people would name their own region first. So in a conversation with a real person, "Where are you from?" travels better than any label you supply yourself.