The tester works in four steps: you type in a call-to-action (CTA), the short instruction that tells the reader what happens next, add a line of context if you have it, read what it finds, then weigh that verdict against three alternatives it builds from your context.

1. Enter your CTA. Type the phrase as it will appear on the button or link, for example "Start your free trial" or "See pricing". The tester reads only what you give it, so a phrase copied straight from your draft page gives a more useful result than one typed from memory.
2. Add page context, if you have it. A sentence describing what the page offers and who is reading it helps the tester judge whether the CTA fits, and it feeds the three alternatives the tool builds afterwards. This step is optional: the tester still checks verb strength, specificity and length without it, but it cannot generate context-matched alternatives if you skip it.
3. Read the verdict. The result shows which checks the phrase passed and which it failed, and why: a weak verb like "click here" gives the reader an action with no destination, while "Send your brief" names the outcome directly. The verdict is a set of checks against known CTA patterns, not a guarantee that the phrase will work on your page, so treat it as a second opinion rather than a ruling.
4. Compare the alternatives, then choose. None of the three generated phrasings is automatically the right one. The version that fits your product, your reader and the sentence around the button is the one to use, even if another scores higher.

Run the same CTA through again after you edit it. A small change, swapping "Submit" for "Send your details", can move a phrase past a check it failed the first time.