Odd question. There is no similarity between the two at all, other than sounding somewhat similar.
Tattle has one meaning. To tell a person with authority about a very, very minor bit of wrongdoing that someone else is doing or has done. It generally involves small children.
"Susie tattled on Bobby to the teacher for eating the class paste."
Tackle has multiple meanings. In contact sports, it means to take an opposing team's player to the ground. In fishing, it refers to the various equipment a fisherman uses, other than rod and reel, to catch fish - lures, extra line, sinkers and bobbers etc. In general speech, it means to 'take on' something. "Joe decided that today was the day to tackle the job he'd been putting off for weeks, cleaning out the garage." When used with 'block', it is a system of two or more pulleys connected by rope or cable, used for lifting heavy objects.