Most books and other printed documents are printed in 11 or 12 pitch Times New Roman font, in black ink on white background, and no spaces between the lines.
This is probably the worst combination for a dyslexic reader!
Times New Roman is a font with serifs - the little twiddly bits at the tops and bottoms and ends of the letters. I am not sure that "twiddly bits" is the correct way to describe them; but I am sure that you will know what I mean.
Reading page after page of text in the format is tiring on the eyes.
When there are web-pages in this format it is even worse - because most computer screens give off a lot of glare and they are usually not set up correctly. Has the computer screen you are looking at now been assessed by a qualified person to ensure that it is positioned correctly to cut out reflections from windows and light fittings? I expect that it has not!
If I keep typing text here to fill up this box you will start to realise what I mean. Just look at all the text boxes on this web page and then decide for yourself which is the hardest to read. I expect that you will choose this one!

Using Arial or Helvetica fonts in a blue or dark blue text colour makes the text more readable.

These fonts are sans-serif - they do not have the twiddly bits.

The whole thing can be made more readable by using a non-white background or by printing on to coloured matt paper.

I have heard that printing on pale blue or cream paper can help some dyslexics.

You could also use the Bold version of the font.

For displaying text on computer screens you could even reverse the colour scheme so that you have a light coloured text on a dark background.

This will help to reduce glare from the screen.