You can best help other forum members by commenting on their posts, especially on things that need to be improved. When you notice something that you know is not grammatical or idiomatic Arikara you can comment on it and suggest improvement. However, good feedback has to be backed up with reference. Unless you have an advanced proficiency level, you can’t simply say “this is how it should be” or “this is how I think it should be”. What you have to say is “I think this needs to be improved because it doesn’t match the usage shown/heard here: LINK/SOURCE DESCRIPTION”.
For instance, many members learn words and their usage in the Word of the Week section and they practice grammar rules in the Grammar of the Week. When you notice mistakes in things that you have already learned through these activities, you can point the errors out together with links to the relevant posts. By doing so you are not only helping others to learn Arikara but you are also improving your own proficiency.
In this way you would help to build the community of learners. The entire forum as well as each and every member, including you would benefit from this.
Remember, your feedback is good feedback only if you support it with reference. The reference can be to the Arikara Online Dictionary, to an authoritative post in the forum, to a text (by a native speaker) or to one of the reliable textbooks.