"I'm gonna take a shower" - slangy. "I'm going TO take a shower" - the clear way to say it. "I have a shower" - this indicates a regular habit, eg. "I have a shower twice a day."

You could also say "I'm going to shower."

I am going to 、 I'm gonna 這兩個句子都是完全一樣的，每一個字都在裡面。只是第二個是口語讀音來的。 正： "I will have a shower", "I am having a shower", "I want to have a shower" 誤：“I have a shower" "to have"、”having"表示continuous action ( 『～著』 )，『i have (something)』這個have的時態只能表達『擁有』的意思。