when you are creating a new post and you about to paste a html code to your post, check beside compose tab at the top of your new post box, click Edit HTML.
Paste the code in the box below in your Edit HTML tab, now go back to compose, you should find the html box in your compose tab, fill in the html code you want paste.
If you want to use a box with border as shown below, use the code in the box below.
<div style="font: 16px/26px durodola, ridwan, olabode; height:120px; overflow: scroll; width: 500px;border:3px solid black;">
Enter your text here</div>
<div style="font-family: verdana,arial,sans-serif; font-size: 10px;">
<a href="http://www.ittrainingcoursesinbangladesh.blogspot.com//">Get it</a></div>
<div style="font: 16px/26px durodola, ridwan, olabode; height:120px; overflow: scroll; width: 500px;">
Enter your text here</div>
<div style="font-family: verdana,arial,sans-serif; font-size: 10px;">
<a href="http://ittrainingcoursesinbangladesh.blogspot.com/">Get it</a></div>
Remember : Both the code highlighted in Red can be change to your desired height and width.Enter your text here</div>
<div style="font-family: verdana,arial,sans-serif; font-size: 10px;">
<a href="http://ittrainingcoursesinbangladesh.blogspot.com/">Get it</a></div>