Can someone please explain to me how Texas can sue 4 other States for counting mail-in ballots?  ?

Texas can't.  Texas AG Paxton is vying for a presidential pardon since the FBI just served Paxton with a subpoena and Paxton had previously been indicted on fraud charges.

In Texas, you are not allowed to have sex with someone without their consent.

The lawsuit is about improperly changing the laws that allowed votes to count that would not have otherwise been counted.  The laws were changed unconstitutionally.

Because Texans voted by their votes didn't matter because these other states broke the law. Texans were disenfranchised because these other states allow illegal votes.

I live in Pennsylvania and used to be proud to have lived most of my life in Philadelphia.

The bottom line is that tRump thought that he had overthrown the American government in 2016 and that he's now the king of America (he and his criminal family are the only people who get to call him "king" and "your majesty."   So being the king, he sees being kicked out as a coup--a revolt to overthrow King Shitgibbon.   He's pissed at all the Americans who voted against him.  He's replaced some military and other top people that he expects to put down the riots if he tries to continue his attack on America.    Texas does NOT dictate election procedure in any other state.  SCOTUS is going to spank him and send him on his way.

Texas doesn't have the legal authority to do that.  

In fact, Texas (along with the other states now involved) has NO legal standing to sue the swing states because of their election procedures.  The suit will be thrown out; the Supreme Court will not bother with it; it will not grant a writ of certiorari.

Legal experts are laughing at the whole, pointless exercise, calling it "the dumbest lawsuit yet" in this whole ridiculous effort to overturn the election. It's basically just a stunt. There is no violation of the Equal Protection Clause.

Technically anyone can attempt to get their case heard by the SCOTUS. Everyday shmoes have to get their case taken through the system working their way up until they get to the Supreme Court. States can bypass that because there are no courts between the states except SCOTUS. Those cases are supposed to be due to some sort of connecting issues. Borderlines or shared bodies of water issues, etc. In this strange time, who knows what will happen. Most legal precedent says this is not an issue for the SCOTUS. But there have been a lot of things decided by “beliefs” and not facts lately. So until this coming Monday. Who knows?

The claim is that mail-in ballots somehow make it impossible to detect problems like dead people voting, which is false. You see, there is something called "voter registration" which can be verified against vital records and drivers' licenses and can be used to check mail-in ballots. Duh. The Texas state legislature actually does not get to decide the laws in other states. Duh. This case is duhmb. Gary--love how you oversimplify the INTERPRETATION of state law by the STATE COURTS (funny how that works). Anything you don't like's gotta be unconstitutional, eh? Intellectual integrity is you.

What Texas has is called "Lack of standing" which means they will lose.