I enioyed the pleasant evening with my friends.
= I enjoyed the pleasant evening (which/that I spent with) my friends.
= I enjoyed the pleasant evening (I spent together with) my friends.
注：/ 表示可以任意选用其一；
变化采用定语从句,关系代词which/that代替先行词evevning,在定语从句中做spent的宾语,所以关系代词也可以省略.