The foreign section (sa106) covers all types of foreign income and gains.
Capital gains and Income tax are two separate taxes and are calculated separately.
If the combined sum of your UK dividends and foriegn dividends is below £2000.00, you can declare the foreign dividend in box 4 of SA100.
If you want to claim a foreign tax credit against the foreign dividends, then you need to declare the foreign dividend in SA106 instead. It is the same with interest at box 3 of sa100.
Have a look at the guidance on capital gains tax, as it equally applies to foreign capital gains -
Capital Gains Tax
All parts of a capital gains calculation on the disposal of a foreign asset, must be in pounds sterling, using the official exchange rate in place at the time.