If you already have a logo, below is how you add it to the site.
If you don't have a logo, you can get a cheap one for $10-$25 here. Ask for the dimensions 340px by 80px.
Add your logo:
Step 1: In Wordpress, go to "Appearance", then "Customize". Then choose "Theme Options", then choose "Logo"
Step 2: Click "Select Image" and grab your logo from your files. Click publish.
Add your Favicon, Site Title and Tagline.
A favicon is the small image you see in browser tabs and bookmark bars. Most website owners use the icon from their logo. The file should be square and at least 512 x 512 pixels.
Step 1: In Wordpress, go to "Appearance", then "Customize". Then choose "Site Identity".
Step 2: Under "Site Icon", choose "Select Image". Choose your image from your files. Click publish.
Step 3: While you're in the "Site Identity" section, change your Site Title and Tagline. This is what shows up next to your website icon and what Google will display in the search results for your homepage.