Below you can access past papers for GCSE and IGCSE. There is a comprehensive set of higher tier past papers for the Edexcel IGCSE including the new 9-1 papers and the older papers. For the other GCSE boards there are just papers relevant for the new 9-1 syllabus. Many of the papers, especially for the IGCSE, also have video solutions accessible via YouTube.
I have also created a page here linking to all the videos I have made working through full or partial past papers from various boards:
Note, there is also a separate page here of exam questions by topic for the Edexcel IGCSE, but many topics will be relevant for other exam boards too!