I am not an advanced speaker of English. I usually make grammar mistakes. For this reason I want to ask questions related to grammar aspects, grammaticality, meaning of phrases and sentences. I would not like to be upset about closing of my questions or downvoting. Answer please whether or not I can ask such questions here in the English Usage & Language Section . Maybe I should go to the English Learners Forum which low level learners usually visit?
The short answer is yes; though I would not characterize ELL as for "low-level" anything.
Because most of their participants are studying rather than using English, and so have access to textbooks on grammar and conjugations and so on, ELL actually usually has more technical explanations of grammar and syntax, and uses more obscure terms of art, than EL&U1. As a native speaker, I can genuinely tell you that half the time I have no idea what they're talking about over there.
EL&U is oriented more towards native and fluent-to-the-point-of-being-native speakers, and questions which would be interesting to them.
So, quick sniff test: if you're trying to sound like a native speaker, use ELL.
1 But when EL&U gets wonky, it gets really wonky.
For basic clarifications on grammar and understanding the meaning of words in context, you probably would find the best fit on English Language Learners. The site is geared toward people who are learning English.
If you feel you are quite fluent in English, and the kinds of grammar and meaning questions you have involve unusual syntactical structures or archaic meanings of words or the historical journey of a particular construction, you are more likely to get a comprehensive answer here on EL&U.
If you have a specific question and you aren't sure which site to post on, you can either post it one place and ask to have it considered for migration if it's a better fit on the other site (moderators can move questions between sites), or you can post on either site's Meta and ask if the community thinks the question belongs there or here. Hopefully, it won't take you long to get a feel for which site is most appropriate for the kinds of questions you have.