What is ordered and unordered list?enlighten me plz....

Answer 1

an <ol>represents a sequence, whereas <ul>represents a set. Rearranging the items in an ordered list changes the list's meaning. Rearranging them in an unordered list does not.

This is a good rule-of-thumb for which type of list to use. If changing the order of the items makes the list incorrect, you want to use <ol>. If the order doesn't matter, use <ul>.
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Answer 2

ordered list example:
1. item 1
2. item 2
3. item 3

and unordered list example:
• item 1
• item 2
• item 3