A quick read you can get through; and gets lots of the fundamentals, you can probably get through it in a sitting or two.
https://ia601403.us.archive.org/35/items/sikhreligion035165mbp/sikhreligion035165mbp.pdf
Of course the Shri Guru Granth Sahib is the prime scripture and guiding source of all Sikhs
also lookup Japji Sahib, Asa De Vaar, and Sukhmani Sahib all of them have tons of translations.