I am US person and a Swedish citizen. Is there any special guide? How buying foreign property and paying mortgage are handled? Any tips for avoiding double taxation?thx!

@bkamrani , assuming  that by "US Person" you mean that you are  US Resident ( Green Card ) / Resident for tax purposes--- (a) there is no specific restrictions/ rules for owning / purchasing foreign  real-estate i.e. you are treated the same as a US citizen and most as if the asset was in the USA.  (b) a second home in any country is treated as a second home in the USA i.e. mortgage interest and property taxes  are deductible when you itemize within the limits/rules applicable to US second home -- SALT limitation and mortgage principle balance limitations apply;  (c) if you rent out the  property then you report gross income, expenses, taxes , insurance etc. etc. on schedule -E just as if the property was in the USA, the only exception used to be the useful life for depreciation ( 39.5  vs 27.5  for US props. ), but has been modified by TCJA in 2018.  If the local taxing authority charges an income tax for the rental income then that amount could be  eligible for foreign tax credit or deduction.

This is the general layout -- does this help or do you need more  info ?  If you do please also tell me  how you plan to use the property ( as personal home or income property ),  type of property ( residential or commercial or what )?