<ul> it means unordered list which generates the bullet list. And <ol> it means ordered list which generates the number list.
For Example, if you want to change the bullet list then there is the css property "list-style-type" and its value is "circle","square","disc" and "none" for <ul> tag. And for <ol> list there is the css property "type" and its value is anything you want to start with.
Ex:
<ol type="1">
<li>Coffee</li>
<li>Tea</li>
<li>Milk</li>
</ol>
The list will start from 1.
<ul style="list-style-type:circle;">
<li>Coffee</li>
<li>Tea</li>
<li>Milk</li>
</ul>
The list will start from circle.
I hope this will help you.