le vs guo

Can someone explain or refer me to a site that explains the difference between le and guo when dealing with past time?  Also the difference in position of le, i.e. right after the verb or near/at the end of the sentence.  Thanks very much.  Mike

Both 了 (le) and 过 (guò) are technically aspect particles. 了 (le)  indicates that the action is complete when used with active verbs. When used with stative verbs (I feel bad), it indicates a change in state. Note that one can talk about things in the past without using 了 (le) provided it is clear from the context, e.g. you indicate that you ate lunch yesterday.

I think you use 过 (guò) to talk about things in the past, like "I have been to China", or "Have you ever been to China".

There are many more uses for both aspect particles. Here are some references.

了 (le) 
https://resources.allsetlearning.com/chinese/grammar/Expressing_completion_with_%22le%22

过 (guò)
https://resources.allsetlearning.com/chinese/grammar/Expressing_experiences_with_%22guo%22

Grammar points in general (see Particles section):
https://resources.allsetlearning.com/chinese/grammar/A2_grammar_points