I would like to know how new family lines can be added to my tree when I know they are not my ancestors? Some of the people I have never heard of.
I keep getting Andrew Jackson Skidmore updates. He is NOT my relation. My relation is Andrew Coldwell Skidmore born August 1840 in Harlan County, Kentucky. How do I fix this problem?
I would like to know that also. It's frustrating.
The Family Tree on FamilySearch is an open-edit collaborative tree. The answer to "how new family lines can be added" is "the same way you can add new family, by adding relationships and profiles". The answer to the underlying "why were these family lines added" is generally "because a fellow user of the site believed them to be correct".
If that fellow user was wrong in that belief, the good news is, it's open edit: you can fix errors yourself. You do not need permission or agreement from anyone.
Here are a few articles from the Help Center that might be helpful:
The World’s Largest Shared Family Tree
How do I see what changes were made about a person in Family Tree?
How do I undo an incorrect change in Family Tree?
How do I undo a merge in Family Tree?
How do I correct parent-child relationships in Family Tree?
How can I prevent other people from making inaccurate changes to Family Tree?