If you are not employed by any entity, to complete online surverys, it is very likely that your earnings from online surveys, is self employment income. If that is the case, in section 3 - tailor your return, please select the option for self employment. Section 4 will allow you to complete the self employment section. Class 2 and class 4 national insurance is payable on self employment income above the threshold.
Self-employed National Insurance rates