On his site Sameer Borate gives you a quick tutorial on how to migrate your WordPress site to HTTPS to help secure the communications between it and your users.

Finally, after much deliberation, I decided to move my blog to https. For the past few months I had encountered articles pointing that google gives a higher ranking for sites served over https. I had decided against https as I was afraid it may slow down by blog. However, the [a message about Chrome's HTTP/HTTPS support] from google forced me to take the issue seriously and finally move to https.

[...] Luckily during the same time Godaddy was offering SSL certificates at a discounted price. So taking this as a sign I bought the SSL certificate and moved my blog to HTTPS. Surprisingly installing SSL on Godaddy was a breeze. There was no configuration involved and the SSL certificate was applied within a few minutes.

He assumes that you know how to get the certificate installed, so that part isn't covered. He does cover the shift of the WordPress site over including changes that'll need to be made to web server and WordPress application configurations. He ends the post briefly talking about any speed difference he saw with the site (hint: not much).