区别就是swimming是动词swim的现在分词形式，中文意思是v. 游泳漂浮旋转（swim 的 ing 形式），adj. 游泳的游泳用的善于游泳的晕眩的，n. 游泳目眩
She's never liked swimming.她从不喜欢游泳。
We went swimming very early.我们很早就去游泳了。
It was too chilly for swimming.
“swim”动词原形，作谓语，用于一般现在时
“swimming”动词的现在分词，1）作宾语，用于谓语之后2）跟在be动词之后，用于现在进行时3）作定语，修饰名词，强调其功能，意为【游泳用的】。
swim是动词，只能做谓语
swimming可看成动名词，即名词，可作主语、be swimming作谓语，swimming还能做伴随状语
例如: He's thinking of something，swimming in the pool.
swimming还能做后置定语，修饰前面的名词
如:Bread is eaten by a fish swimming in the pool.
如:. I usually swim a few laps as warm-up during practices.我一般都会在训练中先游几圈作为热身。
She swam the 400 metres medley ten seconds slower than she did in 1980.她400米混合泳的成绩比其1980年慢了10秒。
My hobbies are painting and swimming.我的兴趣是画画和游泳。
注：swim的现在进行时同样是swimming，不要把它和作为名词的swimming搞混了。
如: He is swimming right now.她现在在游泳
