user=> (def my-list (list 1 2 3 4 5))

user=> my-list
(1 2 3 4 5)

user=> (first my-list)
1

user=> (nth my-list 3)
4

user=> (conj my-list 100) 
(100 1 2 3 4 5)

user=> my-list 
(1 2 3 4 5)

user=> (def my-new-list (conj my-list 100))

user=> my-new-list
(100 1 2 3 4 5)

user=> (cons 200 my-new-list) 
(200 100 1 2 3 4 5)

user=> (def my-vec [1 2 3 4 5 6])

user=> (conj my-vec 300) 
[1 2 3 4 5 6 300]