Anyone would get annoyed if they read articles, letters, notes, etc.
written in bad grammar.
Using very good grammar, correct spelling and punctuation will offer you of a trust among your readers.
It would make you appear more expert writer than if you are making mistakes especially the common ones.
That is why if you want to be a good writer you need to enroll to an English language class.
Is this true? Honestly, yes it is true! That is if you have the time and money to do so.
But do not fret; do not let this be a reason not to learn correct English grammar.
You are blessed you know why? Because you can avail of grammar software on grammar websites for free! Yes it is absolutely free! It is possible that you will be doubtful if these websites can really help you learn to write correct English grammar.
You might also be asking what you can get out of this free grammar websites.
Let us take a peep:

• First and foremost, you get to learn proper English for free
• The grammar sites are always updating.
  Whenever there is new information, the manufacturers would always update their site.
  
• Aside from having up-to-date information, all of the basic information in English grammar are strictly followed.
  
• Usually, these websites used the natural language processing technology.
  This is the latest technology when it comes to proofreading.
  You can proofread your article at the same time learn how to proofread.
  
• You get to use varied lessons from different websites.
  Meaning your scope of lesson is not limited.
  
• You get to do instant hands on.
  Meaning you can instantly use what you have learned, thus it will make your learning more progressive.
  
• You can learn within your own pace.
  No more worrying if you have learned or not, teachers will usually proceed to the next topic whether you like it or not so they can follow their lesson plan.
  Here, you have all the time to learn and learn and learn.
  
• You can learn any time and anywhere you like.
  You are the boss!
• You are assured to learn more from grammar websites than learning the conventional way.
  

Whether you chose to go back to school or choose to learn English online, it is really your choice.
Whatever suits you best then do it! But if you are to ask our advice (me and other satisfied users), then choose to learn online where you can do other things than just learning.