nest the tags.
<b><h1>words</h1></b>
That is the old way of doing things, but it's the easiest way to do it when first learning. There are 6 universally support <h1> through <h6> with the lower number being the BIGGEST.
Now the new way would be to wrap this in span tags
<span id="headerText">Hello</span>
and then format it with a style sheet
<style type="text/css">
#headerText
{
font-weight:bold;
font-size:30px;
}
</style>
or instead of using the id attribute, which must be unique per page, set a class, and then use it over and over:
<span class="name">Jim</span>
<span class="name">Bobby</span>
<span class="name">Susan</span>
<span class="name">Jesse</span>
then in the stylesheet use
<style type="text/css">
.name
{
font-weight:bold;
font-size:30px;
}
</style>
note that we've now used the . (period) before the class, where we otherwise use the # (octothorpe) before the id. There are many CSS styles, the advantage of classes is consistency and ease of changing, if you have 30 names on a page, all you have to do to change them all is change the stylesheet.