It is understandable that one would be confused about the meaning of connotation because that word is, in fact, used in two different senses.
In one sense, the connotation of a word, say x, consists of the attributes in virtue of which we say that it is true that something is x. In this sense, connotation is used together with denotation. Each entity of which it is true that it is x belongs to the denotation of x; all xs in the universe thus constitute the denotation of x. When we are asked whether something is x, we think of the attributes that constitute the connotation of x and consider whether the thing has these attributes. If it does, we say that it is an x, if not, not. The connotation of a word thus determines its denotation. Connotation and denotation were widely used in these senses in philosophy under the influence of John Stuart Mill, but in the current philosophical literature one is more likely to see intension (with an s) and extension used instead. A dictionary definition of a word strives to articulate its connotation, in this sense.
In another sense, however, the connotation of a word consists of the associations that the word usually carries, but that are not a part of its connotation in the first sense. Connotation, in the second sense, of x does not determine whether it can be truly said that something is x, but it is relevant to whether it is apt, polite, illuminating, or awkward, offensive, distracting to say that it is x. Dictionary definitions do not capture the connotations, in the second sense, of words, although some dictionaries may supplement the definitions with usage pointers that include some indications of the word's connotation.
For example, the connotation, in the first sense, of spinster is being an unmarried woman. Whether it is true that somebody is a spinster is determined by whether the person is an unmarried woman. The word is, however, strongly associated with certain assumptions about what unmarried woman are like, and with certain attitudes towards unmarried woman. These associations constitute the connotation, in the second sense, of spinster. Because of this connotation, most people will nowadays avoid using the word spinster, even when it is true that somebody is a spinster, according to the dictionary definition.
When one encounters the word connotation in a present-day text, it is more likely that is is used in the second rather than the first sense, unless the context indicates otherwise.
Connotation in the first sense, is a matter of semantics, while connotation in the second sense is a matter of pragmatics.