This completely depends on your skill-level and what theme you’re using. Let’s take the Twenty Eleven Theme for example (default in current WP version).
If you look at the source of the homepage, you’ll see the body element has the following:
<body class="home blog two-column right-sidebar highlander-enabled highlander-light infinite-scroll">
That is a bunch of classes that you can use to individually style top-level elements. For example, if you wanted post titles only on the homepage to be larger, you could do something like:
.home.blog article .entry-title { font-size:100px; }
As mentioned, CSS knowledge is needed, but relatively small changes can be done by a web developer pretty quickly.
If your question is “how do I make these changes”, these would be typically defined in styles.css within your theme, but it is advisable to Create a Child Theme so you are not editing core WordPress files. Thanks!