Hi Faith
As already mentioned WAT is probably the quickest and easiest way to get up and running.
Also maybe look at some of the bookmarklets at the link 49 Accessibility Bookmarklets You Can Use For A11Y Testing • DigitalA11Y which may help.
What I would consider however, and again this has been mentioned, is what you are trying to achieve. As with all testing, tooling should support your testing goals not be a complete solution. Have a read and explore the WCAG 2 guidelines (WCAG 2 at a Glance | Web Accessibility Initiative (WAI) | W3C) and consider them in any manual testing you do.
Speak to developers and product if possible and understand what, if any, consideration for accessibility has been included in designing/developing the product. Keep potential users and disabilities in your mind as you test – remember accessibility is about being able to use the product.
I’ve been working on a mnemonic for accessibility testing identifying the things that should be considered for effective and inclusive accessibility. BUDI.
Build – Has the product been designed and built with accessibility in mind. If so what has already been considered?
Users - Accessibility is about users and how easily they can use the product. What do you know about your users?
Diversity – Disabilities and challenges are diverse and true accessibility needs to consider as much of that diversity as possible.
Inclusion – If you really want an accessible and inclusive product then you need inclusion in your activities and teams.