Two kinds of SaaS directory
The top of this list is review marketplaces: G2, Capterra, SourceForge. They carry the highest authority on the whole site, they rank for '<your category> software' searches, and they are free to claim. What they don't do is rank your listing until customers write reviews, so the profile is worth creating on day one and worth promoting once ten customers will vouch for you.
The rest are listing directories: a form, a review, a page with a link. These publish faster, ask for less, and the followed ones move Domain Rating the week they go live. Work them top to bottom by DR.
What to have ready
A category you can defend, since SaaS directories organise by it and reviewers compare you against the neighbours. A tagline under 60 characters, a 200-word description, pricing in one sentence with the free tier called out, a logo at 512px and three product screenshots. Review sites also want a company profile: founding year, headcount band, and a support email on your domain.
The free rank plan writes the listing copy for you, sized per form, and puts the SaaS directories that fit your product in order.
What to expect
Listing directories go live in a day to three weeks. Review marketplaces approve the profile within a week, then nothing visible happens until reviews arrive; ask early customers directly and expect one in five to write one. Traffic from category pages on G2 and Capterra is small but the intent is the best on the internet: people there are choosing software this month.