Hi carlos.calroy,
Do you mean how you would declare your dividends from shares you own?
Please have a look here:
Tax on dividends
Which advises you do not need to report your dividends to HMRC, if you are within the dividend allowance.
If you dispose of shares, then you may have a capital gain or a capital loss.
If your capital gain is more than the annual exempt allowance:
Capital Gains Tax rates and allowances
Then you need to report the gains using the online realtime service here:
Report and pay your Capital Gains Tax
You do not need to report capital gains if they are below the annual exempt amount for the whole tax year.
Capital gains losses, must be report in writing to HMRC, along with supporting eveidence.
Thank you.