- This expression means that you are not understanding the main objective of a discussion. To be it simply, it is another way for someone to say that you do not understand what is being said.

let's hear some examples before my legs turn to jelly --

In order to understand the phrase you posted, it would be helpful to understand the context. Generally the expression "to turn [some limb] to jelly" means that that particular limp or set of limps are fatigued . Since I do not know the context of this phrase, it is difficult to provide you with a clear definition of the phrase. Despite the lack of context, generally this phrase would be said in a situation where two or more people are in discusion and also the use of the expression before my legs turn to jelly suggests the people are in a standing position. Maybe Person A brought up a point and Person B wanted Person A to provide him with examples to illustrate this point. There may have been a long pause and so Person B stated that he wanted Person A to provide examples before his legs turned to jelly.

All in all, these two phrases that you provided are used in different contexts and also have entirely different meanings - to the point where the signification of the two phrases are not the same in the least.

I hope fhis explaination helped