Pandas dataframe shows values as 'NaN'
<p>I tried to put columns on the dataframe like following;</p>

<p><a href="https://i.stack.imgur.com/zCcQJ.png" rel="nofollow"><img src="https://i.stack.imgur.com/zCcQJ.png" alt="after I checked it, tried to add columns"></a></p>

<p><a href="https://i.stack.imgur.com/feVdD.png" rel="nofollow"><img src="https://i.stack.imgur.com/feVdD.png" alt="but all contents changed into &#39;NaN&#39;s. how can I solve it?"></a></p>