It is similar to adding a tag cloud in wordpress, but in wordpress a single addition of the widget to your desired place clears the problem and puts the tag cloud for you.
Here, for a blogger platform blog, here is the procedure to do that -

Go to your Blogger Dashboard

Go to Blog Settings

Select Layout in the top options menu

Add Label Widget by Selecting option through “Add page element”

You can choose whether to have the labels randomly or sorted alphabetically.

Now you are half done. Go to Edit HTML section, and search for the following -

<b:widget id=’Label1′ locked=’false’ title=’Labels’ type=’Label’>

Replace that code with the following -

<b:widget id=’Label1′ locked=’false’ title=’Label Cloud’ type=’Label’>
<b:includable id=’main’>
<b:if cond=’data:title’>
<h2><data:title/></h2>
</b:if>

<div class=’widget-content’>
<style type=’text/css’>”;
#labelCloud {text-align:center;font-family:arial,sans-serif;}
#labelCloud .label-cloud li{display:inline;background-image:none !important;padding:0 5px;margin:0;vertical-align:baseline !important;border:0 !important;}
#labelCloud ul{list-style-type:none;margin:0 auto;padding:0;}
#labelCloud a img{border:0;display:inline;margin:0 0 0 3px;padding:0}
#labelCloud a{text-decoration:none}
#labelCloud a:hover{text-decoration:underline}
#labelCloud li a{}
#labelCloud .label-cloud {}
#labelCloud .label-count {padding-left:0.2em;font-size:9px;color:#000}
#labelCloud .label-cloud li:before{content:”" !important}
</style>
<div id=’labelCloud’/>
<p align=’center’>
<script type=’text/javascript’>
var cloudMin = 1;
var maxFontSize = 25;
var maxColor = [0,255,0];
var minFontSize = 10;
var minColor = [0,0,0];
var lcShowCount = false;
// Don’t change anything past this point —————–
// Cloud function s() ripped from del.icio.us
function s(a,b,i,x){
if(a>b){
var m=(a-b)/Math.log(x),v=a-Math.floor(Math.log(i)*m)
}
else{
var m=(b-a)/Math.log(x),v=Math.floor(Math.log(i)*m+a)
}
return v
}

var c=[];
var labelCount = new Array();
var ts = new Object;
<b:loop values=’data:labels’ var=’label’>
var theName = “<data:label.name/>”;
ts[theName] = <data:label.count/>;
</b:loop>

for (t in ts){
if (!labelCount[ts[t]]){
labelCount[ts[t]] = new Array(ts[t])
}
}
var ta=cloudMin-1;
tz = labelCount.length - cloudMin;
lc2 = document.getElementById(’labelCloud’);
ul = document.createElement(’ul’);
ul.className = ‘label-cloud’;
for(var t in ts){
if(ts[t] < cloudMin){
continue;
}
for (var i=0;3 > i;i++) {
c[i]=s(minColor[i],maxColor[i],ts[t]-ta,tz)
}
var fs = s(minFontSize,maxFontSize,ts[t]-ta,tz);
li = document.createElement(’li’);
li.style.fontSize = fs+’px’;

a = document.createElement(’a');
a.title = ts[t]+’ Posts in ‘+t;
a.style.color = ‘rgb(’+c[0]+’,'+c[1]+’,'+c[2]+’)';
a.href = ‘/search/label/’+encodeURIComponent(t);
if (lcShowCount){
span = document.createElement(’span’);
span.innerHTML = ‘(’+ts[t]+’) ‘;
span.className = ‘label-count’;
a.appendChild(document.createTextNode(t));
li.appendChild(a);
li.appendChild(span);
}
else {
a.appendChild(document.createTextNode(t));
li.appendChild(a);
}
ul.appendChild(li);
abnk = document.createTextNode(’ ‘);
ul.appendChild(abnk);
}
lc2.appendChild(ul);
</script>
</p>
<noscript>
<ul>
<b:loop values=’data:labels’ var=’label’>
<li>
<b:if cond=’data:blog.url == data:label.url’>
<data:label.name/>
<b:else/>
<a expr:href=’data:label.url’><data:label.name/></a>
</b:if>
(<data:label.count/>)
</li>
</b:loop>
</ul>
</noscript>
<br/>Powered By:<small><a href=’http://www.bloggerplugins.org’>Blogger Widgets</a></small>
<b:include name=’quickedit’/>
</div>

</b:includable>
</b:widget>

You will see something of this kind -