how do i say things properly without causing misunderstandings?

I suggest you start by using proper capitalization, punctuation and grammar.  Then read a lot to see how others express themselves in writing.

I have always been an avid reader and when I was much younger I fancied I might like to be a writer.  I do write a lot but not for compensation and I read an enormous amount.  I have been told many, many times that I express myself very well in writing.  It is much a matter of practice.

Speaking is very different than writing.  Writing is typically much more formal and sentence structure, grammar and punctuation are much more important.  That being said, sometimes breaking those rules for effect helps make a point or create a tone.  Speaking is almost a different form of communication and includes tone of voice, context, gestures and other more subtle elements.

Practice makes perfect and studying communication and communication skills will help.

This tends to happen when people jump too quickly to a statement without preliminary information to share. Being too anxious to communicate an idea will usually cause confusion. Hurrying to rephrase the topic only makes it worse. Start more slowly and don't feel a need to apologize. An example is your second paragraph. By attempting to rephrase what you already said, you cause further confusion. Say your point as clearly as possible - and then stop.

This is just part of life. If you find you are causing issues then perhaps take a little longer to think before talking. It does happen and it's never deliberate I know. I occasionally don't engage my brain and say something without realising how it will affect others.

For example I went to a hotel, the receptionist says "I think I remember you". Without thinking I said "I don't think I remember you". She said "Oh well thanks". I suddenly realised what I'd said.I do have a friend who is extremely controversial and doesn't think at all before talking. Sadly this means he's lost a lot of friends. The issue there is that he says things without having done any research or thought and comes across as being low intelligence. He's a lovely guy though.

At the end of the day, take your time, stop and think.