Bind an element to two sources

You’re looking for MultiBinding.

Your XAML will look something like this:

<TextBlock>
  <TextBlock.Text>
    <MultiBinding Converter="{StaticResource myConverter}">
      <Binding Path="myFirst.Value" />
      <Binding Path="mySecond.Value" />
    </MultiBinding>
  </TextBlock.Text>
</TextBlock>

With reasonable replacements for myConverter, myFirst.Value, and mySecond.Value.