区别是明显的。前者比后者多了个n,这个n源自not, 是ever的否定。
从词性上讲，它们都是副词。有ever的是可以用在否定句、肯定句或疑问句中，多用于疑问句中和否定句中，有never的是否定句，是not ever变过来的。如：
Have you ever been abroad?
I have never been abroad.
ever在肯定句中有很多种用法，翻译很灵活。例句可以从词典中找：
<<副词>>
(无比较级、最高级)
1 a. 曾经,从来
Have you ~ seen a tiger?.
你见过老虎吗?
Did you ~ see him while you were in Paris?.
你在巴黎时曾见过他吗?
How can I ~ thank you (enough) ?.
我真不知道该如何感谢你?
b. (不) 曾…; 决 (不…)
Nobody ~ comes to this part of the country.
没有人曾经来过该国这个地区
No Chinese tourist has ~ come to this town.
没有任何中国观光客来过这个镇上
c. 曾经
If you (should) ~ come this way, be sure to call on us.
如果你打这儿来,一定要来看看我们
If I ~ catch him!.
要是我逮到他 (我决不饶他) !
He is [was] a great musician if ~ there was one.
如果曾经有过伟大的音乐家,那他就是一个
d. [在比较级、最高级之後用以强调] 以往,迄今
It is raining harder than ~.
雨越下越大了
He is the greatest poet that England ~ produced.
他是英国有史以来最伟大的诗人
2 a. 经常,总是,始终
He ~ repeated the same words.
他总是重复同样的话
He is ~ quick to respond.
他的反应总是很快
→ EVER since
They lived happily ~ after (ward).
从此以後他们就过著幸福的日子