Accrued income (be it interest or dividends) is simply income that has been built up by an asset but at death had not yet been credited to the estate. For example, a bank may calculate interest daily but will usually pay the interest into the bank account quarterly or annually. Therefore at the date of death an accrued income element is normally recorded for an asset.
To record accrued income, ask the asset holder how much accrued income there is. Select the asset, right-click and choose "record income - accrued or actual". All you need do is choose the accrued income type and enter the amount. If you are using the system to fill IHT forms, the accrued income will automatically be added to the death valuation of the asset. Once an actual income receipt is received by the estate for the asset you'll need to record an income entry for the asset. The income entry will include the accrued income amount (and probably a bit more that has built up from the date of death figure).