You can store the connecting string information in your web.config file in two ways:

•  Using <appSettings> Section
•  Using <CustomSection> Section.

Using <appSettings> Section

The predefined <appSettings> section can be placed in any web.config file or the machine.config file. This section is useful for storing name-value pairs of data. An example of the use of the <appSettings> section is as follows,

<appSettings>
       <add key="ConnectionString" Value="myconnectionstring" /> 
</appSettings>

To access the appSettings Value, you need to use ConfiugrationSttings.AppSetting["ConnectionString"]. This uses the NameValueFileSectionHandler, which returns a System.Collection.Specialized.NameValueCollection object. The collection implements the IEnumerable interface so you can enumerate the collection, or read values directly for any valid key.

For more details accessing appSetting value refer this link, 
Accessing the appSettings Section

Using <CustomSection> Section

You can create your own custom sections in a configuration file. The easiest way to do this is to configure one of the pre-existing configuration section handlers, assuming your section uses one of the generic structures such as name-value data, or single tag data. In this particular case you might use the Name-Value data. To do this, you need to use the pre-defined section handlers.

 For example, you can define a section called , <myNameValueSection>

<myNameValueSection>
         <add key="ConnectionString" Value="my connection string"
<myNameValueSection>

To read the data, you will need the following code snippet ,

NameValuecollection config = ConfigurationSettings.GetConfig("myNameValueSection")

For each key in config.keys
       label1.Text = "Key:" + key.toString()
       label2.Text = "Value:" + config[key]
End Loop