What's in a name? For the genealogist, each name is a clue to connections with other people who are on or might be connected to one's family tree.
For generations, given names have come from surnames. When an ancestor has a surname as a given name, think clue. Was it the mother's maiden name? A grandmother's maiden name? Another relative's given name? Only research can answer these questions.
Of course, a parent can just choose a name because s/he likes it. Such is the case for my eldest daughter's name. I visited a restaurant, was served by a waitress named "Maura," and just loved the name. When I married years later and had a daughter, "Maura" she became.
Another fairly common practice is naming a child for one's best friend or a well-thought of neighbor. Namesakes are not always relatives.
According to Emily Anne Croom's Unpuzzling Your Past (2012), there is something of a pattern within naming practices of past centuries:
Eldest son-often named for the father's father
Second son-for the mother's fader
Third son-for the father
Fourth son-for the father's eldest brother
Eldest daughter-for the mother's mother
Second daughter for the father's mother
Third daughter-for the mother
Fourth daughter-for the mother's eldest sister
But one cannot assume that this pattern holds true in all cases as parents are under no legal obligation to name their children after anyone.
This caveat being stated, though, pay attention to recurring given names or middle names within a family group. A repetition of a specific name may be a clue to ancestry or kinship.
Other naming practices affect given names of children. A daughter's name might be the feminine form of her father's or even grandfather's name. Some children are named for famous Americans, movie stars, prominent local personalities, important concepts, such as Liberty, Freeman, or Justice, or even places such as states, "Carolina, Georgia, Florida."
Some names indicate ancestral roots: Siobhan or Brendan may indicate Irish origins; Carlos or Juanita may indicate Latino origins; Amari or Malika may indicate African origins.
Of course, parents may chose or make-up a name for other reasons. Sometimes a nickname becomes a person's given name. For example, my father's name is "Ted," not "Edward" or "Theodore." Parents may have simply liked the sound of a name or wanted to choose something different. Sometimes the names researchers find in records are the result of phonetic spelling. Some may be corruptions of other names or attempts to keep names in a family within a particular pattern, such as names in alphabetical order or names beginning with the same initials.
One cannot necessarily know why an ancestor was given a particular name without further investigation and contemporary evidence. That's what makes researching a family tree fun: Hunting for clues and following the leads!