If you are trying to convince your partner to explore this world, using something as large as a penis is definitely not the way to get started. You should start by getting them comfortable being touched in the area, then move up to using a finger or two, and then, when ready, finally moving up to intercourse. Use the anal fingering to please women.
Until your partner is ready to receive, their anxieties will cause their anal sphincter to tighten, and trying to push through will be extremely painful, so be patient!