NOTE: You need to have a SharePoint Administrator Access to your SharePoint site to perform the steps given below to add a webpart to a SharePoint Foundation 2010 site.

First you need to upload the web part before adding them to your page.

I.   Uploading Web Part.

1.   From your parent site/top level website; click on Site Actions.
2.   Select Site Settings
3.   Under Galleries, click on Web Parts.
4.   Go to Library Tools Documents; click on Upload Document.
5.   Click on Browse.
6.   Select the web part you wish to upload and then click on Open.
7.   Click on OK.

II.   Add the uploaded Web part to your page.

1.   Navigate to the page where you want to install the Web part.
2.   Go to Site Actions and select Edit Page
3.   Click on Add a Web Part where you want to install the new part.
4.   In the Web Part list, select the part you want to install and then click on Add.