Log on to SharePoint as an administrator to the site collection where you want to upload the template. Make sure to browse to the top level site of the site collection.

• Click the Site Actions button ? Site Settings ? Modify All Site Settings

• Go to the Galleries section and select Site templates.

• On the Site Template Gallery page, select ‘Upload’ or ‘Upload multiple documents’
• On the Upload Template: Site Template Gallery page, browse to the .stp file and click OK to upload the file.

• You have now succesfully uploaded the file and are ready to use it.

Creating a new site based on the uploaded Template

• Log on to SharePoint as an administrator.
• Go to the site under which you want to create a site based on the newly uploaded template.
• Go to Site Actions ? Create Site

• On the next page “New SharePoint Site” fill in the field and pick the new template from the ‘Select a template’ section.
• You will find your template under the tab ‘Custom
• Click Create, and now a site based on the uploaded template will be created.

To learn how to export a SharePoint site as a template file (.stp),  please read our article Export a SharePoint site as a Site Template (.stp file)