It´s not creating image of docker by ubuntu

when i run this file on ubuntu firstly i make a make directory and then make a file with name of dockerfile

FROM ubuntu
LABEL maintainer=""
RUN apt update && apt install nginx -y
COPY ./index.html .
CMD [“service”,“nginx”,“start”]
then after these comand in dockerfile and run below command
docker build -t custom-python-image
bash: docker: command not found

Did you install Docker on your machine? On Windows you need Docker Desktop, most others work with open source Docker engine (doc).

Note that best practice is to use an existing dedicated image for a task (see nginx) and not start a new image with a “big” Ubuntu image which has usually all kinds of libraries included.