several作形容词有“几个的，若干的；个别的；各自的”意思，修饰可数名词的复数形式相对于a few，some而言，several较为正式，一般只能用于肯定句，强调“不止一两个”。
（1）I bought several books today.
今天我买了几本书。
（2）There were several problems which tortured the elderly man.
有几个问题折磨着那老人。
（3）They shook hands and went their several ways.
他们握了手，然后各走各的路
（4）She raises several pigs.
她养了好几头猪。
（5）After several visits to Beijing, she had learned a little Chinese.
数次访问北京后，她学会了一点汉语。
（6）There are several holes in the wall.
墙上有几个洞。
（1）a few意为“一些，几个”。在数量上用于肯定意义，强调有一些，后接复数可数名词。
I have a few friends in New York.我在纽约有几个朋友。
（2）a number of意为“许多……，若干……”。强调数量的概念，也可说a large/small number of，后接复数可数名词，谓语动词用复数。
There are number of chairs in the hall.大厅里有一些椅子。
（3）some意为“一些，若干”。带有不确定性，多用于肯定句中，后接复数可数名词或不可数名词。
Some co-workers attended his party.一些同事参加了他的聚会。