This should do your job-
<div style="width:25%;float:left;"></div>
<div style="width:75%;float:left;"></div>
Change the width percentage as per requirement.
Example
<div style="width:25%;float:left;background-color:silver;height:100px;"></div>
<div style="width:75%;float:left;background-color:steelblue;height:100px;"></div>
It will look like below
Hope, it helps !
Otherwise let me know :)