"Sorry I'm not easier to understand" is a good way to acknowledge and apologize for the fact that it is difficult for the other person to understand you. This can be used for any language you are speaking, even your mother tongue. We think quicker than we speak, and sometimes we are not as understandable because of this.
"I'm sorry, I was not clear" is another direct way to let them know that you want to communicate with them, but sometimes it doesn't come out correctly. Clarity happens the more you practice speaking a new language, so people will understand.
"Sorry I'm not easier to understand"（言いたいことが上手伝えられなくてすみません）は、自分の言っていることが理解しづらいことを認め、謝罪する表現です。これは自分の母国語を話しているときにも使えます。人間は話す速度よりも考える速度のほうが早いので、言っていることが理解しづらいことが時々あります。
"I'm sorry, I was not clear"（言っていることが分かりにくくて、すみません）は、伝えたいことがあっても、言葉が上手く出てこないことがあると伝える言い方です。新しい言語では、練習をしていくうちにだんだん伝わるようになってきます。ですから、周りの人たちも分かってくれると思います。
I'm sorry if my English is a little hard-to-understand.
yurinaさん
ご質問どうもありがとうございます。
様々な表現があると思いますが、いくつか自然な表現を紹介します。
・ I'm sorry my English is not the best. （私の英語は[理想](https://eikaiwa.dmm.com/uknow/questions/38724/)なものでないこと、[すいませんね](https://eikaiwa.dmm.com/uknow/questions/83179/)）
・ I'm sorry if my English is a little hard-to-understand.（私の英語はちょっと[分かり難い](https://eikaiwa.dmm.com/uknow/questions/3180/)かもしれませんけど、すいません！）
お好みに合わせて使い分けてみてください。
ご参考にしていただければ幸いです。
Both phrases express that you are struggling with your English. This is okay! By using these phrases you are in a way helping your teacher help you. They now understand you are not comfortable and will help assist you in being more confident.
I'm sorry for not being clearer in my explanations.
This is a way to apologize for being unclear without mentioning that English is your second language. The response of the person listening, especially if they are a native speaker, will probably be to tell you that your explanations are better than you think and they might give you some advice to help you out. Most native speakers are very understanding when non-native speakers struggle. I hope that this helps. :)
An "ability" relates to a skill, if someone is not very skilled at something they can be described as not having a good ability in it. When trying to explain that you struggle at a particular activity you can say "my ability is not very good". Another way to refer to it would be to say you are at a "low level" which explains that you find hard it hard to do something.
"ability"（能力）はスキルと関係しています。何かがあまり上手でないことは、"not having a good ability"と表せます。何かをするのが苦手だと伝えたいなら、"my ability is not very good"（私の能力はあまり高くない）と言えます。
別の言い方としては、"low level"があります。これは、苦手としていることを表します。
If you are deficient in something - could be a skill or an item that is needed - then you are lacking or missing or short of that thing.
"Henry is mentally deficient! He doesn't know what 20 divided by 4 is!"
「deficient in something」は「（技能・物などが）不足している」という意味です。
Henry is mentally deficient! He doesn't know what 20 divided by 4 is!
（ヘンリーは知能が遅れています！20÷4がわかりません！）
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