First of all, you have to make sure you've completed your Settings - in particular, that you've chosen the tax forms you want to file through Taxumo.
Once you're done with that, enter all the income, expenses, and withheld taxes relevant to the period you want to file.
Once done, go to the TAX DUES page:
Go to the section for "Income Tax Returns" -- the cards in this section correspond to tax forms that Taxumo recommends you file.
Simply press FILE NOW on the card that corresponds to the period you want to file.
Upon pressing, you may be presented with the following fields:
Once you've filled out the fields, press PROCEED.
You will be taken to the preview screen where you'll see the data pertinent to your tax filing and how the tax dues were computed.
Afterwards, select the payment method with which you want to pay your tax dues and your processing fees.
Note that if this is a late filing (done after the Taxumo deadline), then the penalties are computed by Taxumo as well. Your filing will be submitted in the next batch that will be sent to the BIR.