In this specific case “I have a poor command of English”. I think they mean to convey that one of their many abilities as a freelancer is to comment for pay on a forum.
So if you wanted to promote your alpaca business on a forum dedicated to IT troubleshooting, she’s your best bet. She would go there and instead of posting:
“Interesting content please buy my totally legit alpacas www.spammylink.com”
As us amateur newbie posters would, she would write:
“Funnily enough, I have an amusing alpaca story related to your hideous HD failure. It turns out that they’re not just cute, but their hair gets everywhere! Here I’s what my HD looked like before and after I cleansed it of all those irritating alpaca hairs www.linkstillspammybutwhatever.com!” possibly followed by something relevant to the discussion to prevent disgusted eye-rolls from other posters.
That this poor seller doesn’t have the wit or the imagination to put a gig up under one of the current categories is a good example of why you probably shouldn’t hire her to do so–that and her poor English. I mean, you could legitimately hire someone to make your dead forum look more interesting and populated, but wouldn’t you want engaging conversation from interesting people?