It is better to speak out rather than keep it in mind when one is angry,.这个是it做形式主语的翻译.
When you are anger,try to speak it out rather than keep it in mind.这个是属于祈使句的句型,用的try to do的短语结构.
When you are angry,don't keep it in mind and split it out !这个也是祈使句,但是具有命令的成分,更符合美式口语的习惯.这里我们也不用speak这种表示了,而是换成更具有美式口语的split out 就是“倾吐出来吧!”的意思